The selection tool is the top most tool on your bar of tools to the left, make sure to have it selected. You can hold ctrl as you click things in the 3D view to select multiple specific things at once. Or in one of the grid views simply drag a box over the stuff you want to select. The grid box selection is less accurate but grabs everything, make sure to adjust it in all of the grid views or you might accidently select just your ground or sky when moving the whole level. Once you have your selection made hit enter, everything you have selected will be red.
If you want video tutorials for hammer or specifically TF2 mapping just ask for direction. We have a mapping tutorial sub forum as well.