I'm relatively new to Team Fortress 2 and I see that all of my weapons have a own level and some of them differ from each other.
Sometimes in matches, I see that some people get an level up on their weapons. How can this be achieved? Is there some achievement which must be reached for a level up on a certain weapon or will they just upgrade if you killed enough bad guys?
What usage can I take from a weapon with a higher level? Does this count in any way? Damage or Reload speed or something like that?