Troops-
The troops are amazing and you can level them up with a labrotory. I will explain the lab in another page but the thing is that the troops do is give you money and power. Power as in trophies. Trophies make you fight better and stronger bases and you aren't recomended to have 3000+ trophies as a lvl 7 town hall. Trophies is something that you get when you win a defense or a good attack. And troops affect both of those things. You will not get anything done when you have no troops since you have to steal money with them. And when you steal money it is to upgrade something.
Barbarian- These guys are the stuff you get first. They are good to a point. They are better together than apart. But thats the point. They will die when you put them together and slpash damage takes them. These guys are best used to distract since they cause so much chaos if used well. They are usually used with archers.
Archers- These girls are the type who don't like to do much you know. They just want to hang back and shoot (and maybe text their GIRL FRIENDS and say wassup ya know). They like loot but not as much as goblins. And they don't do as much damage as barbarians. But they can hit somethning flying and can snipe things to help take it down. So put these awesome girls behind something. They will clean up the other buildings.
Giants- These guys are calm until you show them a turrent or something that shoots troops. Then their fury will be unleashed. These guys are used to take hits since they are strong. Put in barbarians with it since they can help them move up. Its what I do. Then you can put things like arhers, wizards, or a witch to clean up after the giants.
Goblins- These are goblins. They are the weirdest yet coolest troop since they are all about that loot, 'bout loot no trouble. They are something you don't really want to put in as an all troop raid. You want the goblins in as a distraction or something that needs to have a distraction to work.
Balloons- These guys try their best to destroy the defenses just like giants. They hate defenses. They take them out, then you put in ground troops or minions to take out the base.
Wizards- These guys are like the archers. But they are so much better and they have the firepower to take out the strongest things. They are in the back, so distract the defenses to use these better. And they are as slow as barbarians, just so you know.
Healer- these girls heal your troops and they try to heal the first troops you put down.
Dragons-These beasts have the might and the strength to take out any troop and destroy the toughest buildings. Put these guys with the rage spell as a way to make them move faster. And you should take out the air defenses as a precaution.
P.E.K.K.A- No one knows who she is but she can take tons of hits . She has extreme armor. But she will get hurt from the hidden teslas damage since it does double. Her armor is very conductive.
Minions- The first Dark barracks troop you will have is the minion. And it is pretty cool since it is too small for a seeking air mine to find and these do lots of damage for something so small.
Hog Riders- These guys hate defenses so much they jump over walls to get to them. They will smash them to the ground, but not with out help, so you need to help them destroy their base with other troops also.
Valkrie- These girls have the smarts to get in between two buildings to hit two at the same time. They will take down the ground buildings and will have area splash damage to take down more than one troop at one so these girls can be great defenders too.
Golem- These guys live for distracting defenses. They have tons of health and they won't stop trying to go to the defenses. When they die they split into two golemites with half the health and a fifth of the attack damage.
Witches- are the of the magic since they can raise the dead to fight for her. they will distract the turrents while she does her own thing to help.
Lava Hounds- These guys are the golems of the sky since they will distract the air defenses to help destroy the air defense so your minons or what ever can do what they want to the base. When they die they will split into lava pups.
For more comics of troops screwing up go to clashers comics for more information in this link- http://clashofclans.wikia.com/wiki/Clashers_Comic