From an activity's roster, you can add a student into the class in two ways:
New Order: Allows you to create an order on behalf of the client. You can add a new or existing student to the class and record the payment on their behalf. For clients who have initiated orders with you previously, you'll have their credit card information already on file, but if it's a new client or a client who has never initiated an order themselves with you, you'll be able to enter their credit card information. You will be able to use coupons and charge for add-ons as well. Learn more here.
Add Student: Allows you to add a new or existing student to a class without charging them or creating an order. This button is great for free trials or if you have a student who joins the class but doesn't pay.
For both methods, clients will not be asked to answer form fields (as it is an action taken by you, the admin.) To have clients retroactively fill out form field information you can have them go to their Sawyer profile - https://www.hisawyer.com/account/info