How can the president check the congress to make sure they don't have too much power?

Yes. The 'executive order' is a tool that is often misused to improperly take powers that do not belong to the Executive branch or the office of the President.

The veto power.

The President checks congress when he vetoes a bill. Congress can check him if there's a 2/3 majority vote to override his veto. He can also call for a news conference of go onto television to speak...

It can pass a bill over the president's veto

if he vetos a bill they can over vote him and pass it. But if he lets it sit for 10 days it will die.