You can force your affiliates to accept Terms & Conditions when they are signing up to your affiliate program by navigating to Configuration > Affiliate Signup > General tab, and checking the checkbox "Force acceptance of T & C". Once it's enabled new affiliates have to agree with your terms & conditions, otherwise they will not be able to finish their registration.
But as your Terms & Conditions might change over time, your affiliates may not notice it. If you need to make sure that all your affiliates have seen your new updated Terms & Conditions, you can force affiliates to accept T & C every time you'll update them. To do that, navigate to Configuration > Affiliate Signup > General tab, update your T & C in the "Affiliate program Terms & Conditions" field, check the checkbox "Require new agreement to Terms & Conditions", and hit the Save button at the bottom of the page.
The next time an affiliate logs in to his/her affiliate panel, he/she will have two options. Either agree with the new Terms & Conditions or log out from the affiliate panel. That means the affiliate will not be able to access and use their affiliate panel without accepting new Terms & Conditions.
You are also able to check which affiliates have already agreed with your current Terms & Conditions by navigating to Affiliates > Affiliates Manager, and editing your affiliates' grid view to display the column "Agree to terms".