when i started youtube I used Window Movie Maker 6.0, its free and does the job for simple edits. Later down the line I upgraded and got myself Camtasia Studio 7/8 and that helped me with the more advance edits, but it was nothing like adobe or sony vegas, I couldnt do colour correct and professional edits but for what I was doing it helped alot.
Now I used Vegas Movie Studio Platinum 14 on Steam, I will be getting the 15 version soon but I use this to do advance edits and make my videos look professional. personally I recommened you start at the bottom and work your way up, and always look at useful video tutorials when needing help with some aspect of sony vegas or adobe.