Burk, WOT has a learning curve. BroG you're learning about the spotting mechanic.
If a tank on your team 'detects' another tank, their radio range has to be within your range to suddenly see it. Also camouflage plays a factor making it harder to detect some tanks that are behind bushes, using camo nets, and so on. Basically detecting is a comparison of your detect range and their camo rating. The spotting mechanic is how visibility works in this game. As I said, it's not call of duty where they're always there. Typically it's not that bad, but when you go around a corner don't be surprised when they suddenly get detected. Use buildings and such to pop out. A good example would be say I'm 190 yards from you, and your detect range is 200. You should see me...however if I have camo on which improves my 'hiding', against me only I've reduced your detect range for me personally to around 175 or so. This means you can't see me unless you got closer. Not many tanks go for heavy camo. TD's and Lights are usually the ones that go that route. Although end game, TD's are where I hear a lot of the meta has gone.
Also, to earn tanks you get Experience. There's 2 types of experience. TANK experience where you complete a match and get XX points to spend on that tank ONLY. And Free experience which is usually under 10% of the previous TANK experience. Free experience is nice as you can use it on other tanks. I tend to let it accumulate and try to use tank experience as much as possible except maybe to unlock a needed gun or something. That said, credits are needed too. The last part is, you can't unlock the next tank until you've unlocked the portion of the tank tree required to move forward. For example the M4 has a DERP gun in the tree, you don't have to learn it to move on, but the other paths you do. Those unlocks take experience.
Esperatus, On my KV line I went Derp all the way, KV-1 and KV-2 Derps are just fun (especially with a shell rammer). KV-1S I went with that silly over powered penetration gun. Russian gun accuracy is horrid so I don't try to snipe with them much, but brawling can be dangerous (like the KV-1S's armor is paper thin).
My favorite tanks are as follows (I like heavies and like turrets):
T5: KV-1 and PZ-IV (both with derps)
T6: KV-1S and Hummel arty
T7: T29 and GWPanther arty
T8: IS-3 and Tiger II
T9: E75
T10: Haven't decided yet, working towards T57 Heavy, but maybe the T110E5.