how to get appian user name login in the form please ...

You can use the loggedInUser() and the user() functions to display the logged in users name on a form. If you are doing this, just to save the user who completes an action, then you may just want to create a custom output that saves the task owner into a variable.

You can read about the loggedInUser and the user functions here - forum.appian.com/.../Appian_Scripting_Functions.
Hope this helps.

many thinks

Make sure to enable the "Refresh default values every time the task form is viewed" checkbox in the "Other" tab of the form, otherwise you won't get the right username as stated in the documentation.