There are many ways to check a dollar bill's authenticity. Here are some ways to see if your dollar bills are authentic or counterfeit.
Step 1: Hold bill to light
This will work on $10 bills and $20 bills. I don't know if this applies to higher denominations like $50 bills and $100 bills. Please reply if you do know. This will not work on $1 bills, $2 bills, and $5 bills. Hold the dollar bill up to the light and if you see the President's face on the right side of the bill, it's authentic. If you don't see the President's face it's counterfeit.
Step 2: The ink test
This will work on all denominations. This is commonly used to test lower denominations such as $1 bills, $2 bills, and $5 bills. Take a pen and make a streak on the dollar bill. If the ink shows the same color on the dollar bill, it's authentic. If it changes color it's counterfeit.