Some details change every time, such as the client's name or the price. In a text item, tick Fillable by sender at send time and give the field a label, for example "Client name". The field stays empty in the template, and RemoSign asks you to fill it in each time you send.
You can also set a field to fill automatically from the client, for example with the full name, ID number or address. When you choose a client for the document, those fields fill in by themselves. Fields connected to your own details, such as your office name or license number, fill in from your profile.