Hi,
On Object Explorer select Security and then Logins.
Select the user you need to check and then, on the rigth side (Summary) rigth click the mouse and choose "property". A new window will appear with the Server Roles associated to the user and other information.
Choosing Server Roles on the left, rigth clicking the mouse on the summary view and choosing property bring you information about the Roles.
Did it help you?
Regards,
Joao