This "Necessary and Proper Clause" (sometimes also called the "Elastic Clause") grants Congress a set of so-called implied powers—that is, powers not explicitly named in the Constitution but assumed to exist due to their being necessary to implement the expressed powers that are named in Article I. The Bank's existence is a great example of implied powers: the Constitution doesn't say that Congress has the right to establish a bank, but its defenders claimed that one was necessary to carry out the Congress' power to collect taxes. Hope this helps.
