(CNN) — The nation will be watching closely when President Donald Trump reveals his nominee for the Supreme Court Tuesday night.

The jurist’s potential to impact the lives of Americans is incalculable.

Trump’s nominee would replace conservative Justice Antonin Scalia, who died suddenly at a remote Texas hunting resort last February.

The vacancy in the nation’s highest court was followed by the refusal by Republicans to consider Democratic President Barack Obama’s nominee to fill Scalia’s seat.

Here’s why the Supreme Court matters:

Who checks the actions of the president?

If the controversies of Trump’s nascent presidency are any indication, the nation’s federal courts will be busy attempting to resolve future legal disputes.

“That will put the Supreme Court, and potentially this new jurist, at the fulcrum of Trump’s efforts to change life in America,” Joan Biskupic, CNN legal analyst and Supreme Court biographer, wrote Tuesday.

Case in point: Trump’s order last Friday temporarily barring refugees and citizens from seven Muslim-majority countries from entering the country resulted in massive protests and a flurry of litigation.

The part of the executive order blocking entry to people from seven Muslim-majority countries — even if their visas were valid — drew the most criticism. Lower court judges temporarily suspended parts of the order.

The constitutionality of Trump’s sweeping actions will likely be decided by the Supreme Court.

Does the ideological makeup of the court matter?

The nine-member court is deeply divided along ideological lines. Every vote matters.

The dissent of a lone justice can tip the balance on major issues involving civil rights and criminal law.

Scalia’s successor will take the place of a rigid conservative on social issues such as abortion rights, affirmative action and gay marriage. Under Scalia, the court was one of the most conservative in modern times.

“Rarely has there been a moment in American history of such widespread national discord, internal court divisions, and the opportunity for a new tie-breaking justice,” Biskupic wrote.

Trump has expressed his desire for a justice who would reverse Roe v. Wade, which made abortion legal nationwide. He has said he wants states to have the power to determine when a woman has the right to end a pregnancy.

What’s the makeup of the current court?

Four Republican appointees on the bench have generally taken a conservative stance (Chief Justice John Roberts and Justices Anthony Kennedy, Clarence Thomas and Samuel Alito) and four Democratic appointees regularly have been more liberal (Justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan).

But Kennedy’s centrist tendencies prevented conservatives from significantly rolling back abortion rights, or race-based policies intended to enhance student diversity at universities — as allowed in 1978 by Regents of the University of California v. Bakke. Kennedy was also the crucial fifth vote to declare a constitutional right to same-sex marriage in 2015.

He remains on the bench, but he is 80 years old and has indicated to some close friends and associates an interest in retiring. If he were to step down, successive nominations by Trump could transform the court and the law in America.

Ginsburg, who will turn 84 in March, is the court’s eldest justice. Breyer will turn 79 in August.

What is the primary purpose of the court?

The justices serve as the final word for a nation built on the rule of law.

They interpret the Constitution, which involves every aspect of our lives — how we conduct ourselves in society and boundaries for individuals and the government.

As the late justice William Brennan once wrote, “The law is not an end in itself, nor does it provide ends. It is preeminently a means to serve what we think is right.”

When it came to deciding who won the 2000 presidential election, for instance, the conclusions of the Supreme Court ultimately resolved the issue, even though the controversy lingers.

Why was the Supreme Court created?

The first meeting of the Supreme Court was in 1790.

The court is led by the Chief Justice of the United States (that’s the official title). All justices — and all federal judges — are first nominated by the president and must be confirmed by the Senate. They serve for as long as they choose.

The court has occupied its current building in Washington only since 1935. Previously, it borrowed space in Senate chambers in the Capitol Building.

The Constitution’s framers envisioned the judiciary as the “weakest,” “least dangerous” branch of government.

Over the years, the court has often been accused of being too timid in asserting its power. But when the justices flex their judicial muscle, the results can be far-reaching.

Consider cases such as Brown v. Board of Education (1954 — integrated public schools), Roe v. Wade (1973 — legalized abortion) and even Bush v. Gore (2000 — resolved the disputed presidential election).

How does the court work?

Traditionally, each Supreme Court term begins the first Monday in October, and final opinions are issued usually by late June.

The justices divide their time between “sittings,” where they hear cases and issue decisions, and “recesses,” where they meet in private to write their decisions and consider other business before the court.

Court arguments are open to the public in the main courtroom, and visitors have the option of watching all the arguments or only a small portion.

Traditions are observed. The justices wear black robes. Quill pins still adorn the desks, as they have for more than two centuries.

The justices are seated by seniority, with the chief justice in the middle. The two junior justices (currently Sotomayor and Kagan) occupy the opposite ends of the bench.

Before public arguments and private conferences, where decisions are discussed, the nine members all shake hands as a show of harmony of purpose.

Arguments usually begin at 10 a.m. and since most cases involve appellate review of decisions by other courts, there are no juries or witnesses, just lawyers from both sides addressing the bench. The cases usually last about an hour. Lawyers from both sides very often have their prepared oral briefs interrupted by pointed questions from a justice.

How many cases are accepted?

Each week, the court receives more than 150 petitions for review — decisions by lower courts appealed to the high court. Relatively few are granted full review. About 8,000 to 10,000 such petitions go on the court’s docket each term.

Only 75 to 85 cases — about 1% — are accepted.

Court opinions are final. The only exception is the court itself, which can over time overturn its own precedent, as it did with racial segregation. But most justices rely on the principle of “stare decisis,” Latin for “to stand by a decision,” where a current court should be bound by previous rulings.

CNN’s Bill Mears and Joan Biskupic contributed to this report.