Patrick Bateman said:
Where can I see how many kills I need to unlock something?
There are a few ways to get weapons:
1. Achievement milestones. At 10, 16, and 22 achievements as part of a class pack (including the milestone achievements, so it's really 10, 15, 20) you will get a specific weapon. These are the first three unlocks for each class.
2. Item drop. Every 30-70 minutes, you will receive an item drop, up to a maximum of about 10 hours per week. Unused hours of one week carry over to the next, for a total of 20 hours. You just have to be online and connected to a server for this to happen.
3. Crafting system. Most weapons not available through the achievement system are available through crafting. For example, a Scrap Metal and a Sandman can give you a Pain Train. See
http://wiki.teamfortress.com/wiki/Crafting/ for the list of recipes. Basically every weapon with it's own stats except achievement milestone weapons and the two Jumper weapons are craftable.
4. Buy them! Using real dollars.
5. Trade for them! With other users.
6. Specific achievement/bonuses. Preorders of other games, gaining specific achievements in other games, etc, can unlock weapons/hats/misc items in TF2. Ones that have different stats are also available to craft (such as the two Rift weapons, Sun-On-A-Stick and Sharpened Volcano Fragment) but ones that are just reskins are only available through their promotion (such as the Iron Kurtain and the Frying Pan)
Note that other items have their own drop timers (crates are gained in addition to other drops, as are hats, and hats are super-rare).