A more thorough explanation:

The Establishment Clause is a part of the First Amendment of the United States Constitution. It says that the government cannot make any laws that establish an official religion or show favoritism towards one religion over another. It also means that the government cannot show preference for religion over non-religion or vice versa.

For example, the government cannot force people to follow a certain religion or use public money to support religious activities. However, the government can allow religious symbols or prayers in certain situations, such as opening a legislative session with a prayer or allowing religious groups to use public facilities.

There have been many court cases that have dealt with the Establishment Clause. For instance, in the case of Town of Greece v. Galloway, the Supreme Court allowed religious invocations to open legislative sessions. In Lemon v. Kurtzman, the Court ruled against state funding supplementing teacher salaries at religious schools. And in Salazar v. Buono, the Court considered the constitutionality of a large white Christian cross erected by members of the Veterans of Foreign Wars on federal land in the Mojave Desert.

The Establishment Clause is important because it helps to protect religious freedom and prevent the government from showing favoritism towards one religion over another.