To connect a merchant account follow these steps: 

1. Go to Setup
2. Click on Payment Settings.
   
   
   
   
3. Go to Accept Credit Card Payments and click on Connect to Square.
   
   
   
   

If you already have a Square account, you will be prompted to login to your account, otherwise, you will be prompted to create an account.

Fees:
ClinicSense does not charge a transaction fee, so you will only pay the standard rate from Square:

Click to view Square pricing