What does the elastic clause do?

The Elastic Clause is in Article I of the US Constitution, and it states that any powers necessary to complete the powers listed above (the expressed powers of congress), but not necessarily mentioned there, are nonetheless granted to the Congress.

For example: An express power is that Congress can maintain an army. A implied power (powers granted by the elastic clause) would be to recruit, train, and draft citizens into that army. It could also establish military bases to which civilian access was restricted.

The elastic clause has been used throughout US history to add powers to the federal government.

It allows the federal government to expand its powers.