Plain-English Explanation
Freedom of religion has two parts: the Establishment Clause, which prevents the government from establishing or favoring a religion, and the Free Exercise Clause, which protects the right to practice one's faith (or none).
Relevant Provision
U.S. Const. amend. I (Establishment Clause and Free Exercise Clause).
Relevant Decisions
Employment Division v. Smith
494 U.S. 872 (1990)
Held that neutral, generally applicable laws do not violate the Free Exercise Clause even if they incidentally burden religious practice.