What does article 1 of the constitution do?

Section 1 is a vesting clause, granting all the federal government's legislative authority to Congress. Similar vesting clauses are found in Articles II and III, which grant "the executive power" to the President and "the judicial power" to the federal judiciary. The Vesting Clauses thus establish the principle of separation of powers by specifically giving to each branch of the federal government only those powers it can exercise and no others. This means that no branch may exercise powers that properly belong to another (e.g., since the legislative power is vested in Congress, the executive and judiciary may not enact laws).