Show Column Value From Another Table In My Form

I have a table ‘purchase’ that has user_id reference to ‘user’ table. On my _form in creating new purchase, how can I display all the id of the user from the user table? And if it is possible, how can I display the name of the user that has a role as member? Again column ‘role’ and ‘name’ belongs to table ‘user’. Hope someone help me here. Thank u.