share user id in vb.net windows application

what do you mean?

how to use  (user id) for login user in forms  in vb.net windows application

how to store (user id) to use it in all forms in vb.net windows application

check this other question: https://www.experts-exchange.com/questions/28001862/login-and-role-in-vb-net-widows-application.html?anchorAnswerId=38797793#a38797793

Declare it as a variable in a module. Set it on login page and you can use it on any form.

please tell me how with the code

I once made an app that got the current username logged in. In that app I hit a permissions db to decide what they could do, by using the currently logged in username. If this is what you mean, then

My.User.Name

Will give you the current username.