The first thing you will need to do is get a copy of your API Signature from PayPal. Click here
Once you have your API Signature follow the below instruction.
1. Go to WooCommerce and then settings in your dashboard.
2. Click on the Payments tab and then enable PayPal and then click on PayPal to get to the settings.
3. Place a check mark in the box next to Enable PayPal Standard. Enter your PayPal Email (This is the email address that you use to sign into your PayPal account) Enter the email address where you would like the notice to go for a payment that was made with PayPal.
4. Enter your API Signature info that you got from PayPal. Once this is all done click the save button and now your gateway with PayPal should be setup. It’s not a bad idea to run a test order on your site to make sure that it’s working.