On the computer you want to remote control, download "TeamViewer QuickSupport" from TeamViewer. The downloaded file is named TeamViewerQS_en.exe. The program is self-contained so it does not need to be installed.
Double-click on the TeamViewerQS_en.exe file to launch TeamViewer on the computer you want to control.
At the main screen, the numeric ID of that system is listed and a numeric password for that session. Make a note of the ID and password as you'll need that information later.
If you're setting this up on someone else's computer, you may want to create a shortcut for them or place the file on their desktop so they can find it more easily when they need your help. Once you've connected to the computer, a small window with a session list will pop up in the lower right-hand corner.
TeamViewer session list