How to select the entire object on edit mode I need to have further explanations about how to select everything while I'm on edit mode as in this tutorial.

I would like to know how I can select the entire object in edit mode because when I'm on object mode I can select only one part of the object and when I switch to edit mode I can again edit only the part that I have previously selected on object mode. I've tried to do CTRL+G but at the minute 28.11 I saw that it's not the right answer,because she can select each individual piece of the character,but I can't. So,what's the solution ? thanks.
You hit Ctrl-J to join all your objects (they need to be selected). When in Edit Mode hit the A key to select all your points (vertices). You can hit it again to deselect everything. If you want to only select your object, use L.