Putting a menu item on the right side?

I’ve read through some threads about this but I can’t understand the answers enough to apply them to my site. I’m a complete noob with this and don’t know what goes where.

I have the topbar (not the header) with several menu items and one of them is a link to the login page. The problem is that all the menu items start from the left side and are placed next to the previous one. Then there’s a big blank space until you get to the far right where there is the search button (a magnifying glass).

I want to place only the “login” menu item on the right side, of the topbar, just to the left of that search button.

I’m sure it’s easy to do but I have no idea how to do it. Could someone tell me in a step-by-step fashion what I need to do? What files to look in or whatever?

Any help would be much appreciated. Thanks.