They are designing a "training" mode for each class.
you can find the transcripts from the "Meet The..." series on the tf2 wiki.
Nothing you will just have to start all over on the update no damage will be done.
Then spy was created when the game first came out. He is equal in age to all the other classes. His estimated "birth" year is 2007.
The soldier was created when the game first came out. He is equal in age to all the other classes. His estimated "birth" year is 2007.
Then engineer was created when the game first came out. He is equal in age to all the other classes. His estimated "birth" year is 2007.
The demoman was created when the game first came out. He is equal in age to all the other classes. His estimated "birth" year is 2007.
The heavy was created when the game first came out. He is equal in age to all the other classes. His estimated "birth" year is 2007.
The spy was created when the game first came out. He is equal in age to all the other classes. His estimated "birth" year is 2007.
You can be any of the 9 classes and switch at any time, remember that you can upgrade/switch all weapons, hats, misc items and anything else on each class.
All game modes are installed in the one game when you first download TF2. When new game modes are added they are patched into your game and you can play them after you update your client. (Which starts automatically)
well, nobody knows how old he actually is, since he tricked the devil into making him immortal
all your stuff will get deleted.