In your Contract(s), you can have your customer agree to certain areas of your contract. In order to do so, go to Settings -> Contract Templates and select the contract you would like to make these adjustments to. Once you are in the Contract, the variable you would use to add this box is *initials* or %initials% and this will place a box on the Contract that the customer must check off to agree to. It would look similar to this:
The customer cannot move forward with signing the contract until they have selected the box(es) to agree.