I've been playing this since I got my new PC and I've been enjoying it too. I'm writing this as I just got deleted playing a Tier 4 in a Tier 5 match - although I did take a T5 down with me and now its finished I see I ended up middle of the team in score
I'm now at Tier 5 in the British cruiser line, Tier 4 in the German Battleship, Cruiser and Destroyer line, Tier 3 in the French cruiser line and just started grinding the Japanese.
Battleships are the "tanks", they have big guns, slow turrets and are generally slow and sluggish but with lots of armour and hit points.
Destroyers are small, stealthy, fast and agile, but thin skinned.
Cruisers sit in the middle and vary from line to line.
I started off playing the British cruiser line - which I now know is generally not the smartest thing to do. Cruisers aren't as fast or sneaky as destroyers and they don't have the armour to compensate. The British line is different in that they have less hit points but are a bit sneakier. They also only get one ammo type, semi armour piercing, and have smaller calibre guns. This means that while they are good at killing destroyers they are not so good against battleships as the usual cruiser tactic against those (especially if they are a higher tier) is to load the HE and burn them to death. Can't do that with the Brits.
I decided to try the German destroyers because they aren't one trick wonders at early tiers like the Japanese (torpedo boats, bad guns) or American (gun boats, lousy torps) destroyers and they have bow torpedo launchers. However whilst I've managed (somehow) to get to Tier 4 I still haven't learned the art of destroyer combat. I thought I'd enjoy it as I like stealthy approaches in other games, but whilst I can get into trouble I haven't yet mastered the art of getting out, and I get killed pretty quick.
I tried German battleships as I'd already started the grind in order to get on destroyers. Some battleships are better at long range, the German armour arrangement (and poor gun accuracy) makes them good brawlers. I'm not doing too badly, but you must keep an eye out for torpedoes as they don't turn well.
Early German cruisers are $%*&, no other way to put it. But the Tier 4 isn't too bad, so long as you use the AP ammo, the HE isn't particularly useful (unless going against upper tier battleships, your AP bounces so you may as well try to burn them).
My destroyer experience has brought me back to the Brit cruisers. I now play them like I want to play my destroyers, sneak into the fight, run circles around the bad guys and lob torps at them at point blank range. I usually get killed but I usually kill more of them in the process, even when up tiered.
DON'T play the French first time out. Their cruisers are just as bad as the Brits except they don't aren't quite as sneaky. They have the usual mix of AP and HE ammo and they have torps, but unless you know what you are doing you will struggle more than the Brits.
If you want to learn more, I suggest going on youtube. These two links are good for learning tips and techniques and ship comparisons.
https://www.youtube.com/channel/UCxCRnJcVb_CGvKHAOsHNd2g/playlists?disable_polymer=1
https://www.youtube.com/user/cheesec4t/videos
However if you want entertainment you can't go wrong with The Mighty Jingles (I was watching this non-stop when I was off sick for three weeks last year).
https://www.youtube.com/user/BohemianEagle/playlists?disable_polymer=1
Keep an eye out for kjc733. I'm usually playing Co-Op Battles as I still don't feel ready to play PvP.
EDIT - Holy Cow! Tier 5 Emerald in a Tier6/7 match!!! Not going to end well!!