To install the application, first and foremost you need to have the desktop version installed in the computer that you want to access. Once that's done, you'll be able to access the machine and perform any action that you want, since from the iOS terminal you'll have a virtual keyboard available (with a Windows keyboard included) as well as mouse functions (right-click, left-click, and scroll).
In short, using it puts your computer in your pocket. The only thing is that you'll need to have a fast WiFi connection to make it run smoothly, or else you may run into all sorts of problems.
TeamViewer for Remote Control is a really useful tool if you do a lot of traveling, have important projects on your computer, or just want to maintain a connection with your principal machine.