Your character can only hold 3 weapons. Class updates give you 3 new weapons. The loadout system allows you to mix and match those 6 weapons to your preference.
Valve is slowly updating every single character (class as I call them) with new weapons and achievements.The Heavy, Medic and Pyro already got theirs, next up is the Scout.
every milestone gets you a weapon
Milestone...?
Its a miracle that all the hundreds and thousands of TF2 players managed to figure out how to play without coming to post a topic in our Games forum!