To log in, simply type your login ID into the text widget and hit return. You will be prompted for your password, which you should then enter. After a few moments, you should be presented with a desktop, complete with a taskbar at the bottom of the screen. You can launch applications from the Red Hat icon at the left of the taskbar. The other icons in the taskbar launch other applications; you can find out what they are by mousing over them.
In particular, the System Tools menu selection has Terminal as one of its selections; this is probably one of the first applications you'll launch each time you log in. You'll typically launch other applications from the terminal window.