Need some help and explanationFollow

As a level 16 warrior you're missing out on a lot of things. Defensive Stance comes at lvl 20 and Berzerker at lvl 30. The first thing is to find out how you like to play warriors.

At around level 20 you will be entering either the Deadmines or Wailing Cavern, with a group. You will be expected (or not) to be a tank. You may well foul it up immensely. You may be a total success. Either way, you aren't that good, and you aren't that bad. If you're bad, try again until you get good. If you're good, try again until you realise how bad you were. This is level 20, you're a first timer, trying to find out what you like.

You may feel that you would prefer to carry a huge axe, and lay slicy death upon whatever crosses your path. I say: NO!. You're here to find out how you like to play. So, in DMs or WC, you will take a shield and a 1H weapon. And you will use them. You will mocking blow anyone that hits a healer. You will do this with out fail. You may well make an **** of yourself. Take it on the chin, you're a warrior - 'Blame the Tank' is Rule 2 for Instances. But you'll have tried tanking. Only then can you say "Me prefer make Smash!! FullsizeOwl make kill!!!"

Regarding the buttons:
Charge: You'll use this a lot, until you discover ranged pulling. But you'll only use it once, at the beginning of a fight. Whilst your action bar is still relatively empty keep it on there, but not somewhere critical.
Rend: Becomes less useful as time goes by, but it's an attack. It stays. For Now.
Hamstring: (I think you have it) Nice and handy, stops a mob from running quite so fast.
Heroic Strike: An extra attack, next round. This uses rage. It appears like your main attack, but isn't really. Use sparingly, it will drain your rage.
Overpower: Not always lit. When it's lit, hit it.
Shouts: Use as and when: Starting a fight, or when you notice they're not on.

As you get them:
Sunder Armour: Instant, reduces armour. Essential.
Thunderclap: AoE attack. Essential.
Cleave: Like heroic strike, but hits two mobs.
Shield Block: Raises your shield to protect you from a mob.

There are more, they're all documented somewhere.

At your level I'm guessing that your action bar looks like:
1) Charge
2) Auto-Attack
3) Rend
4) Hamstring
5) Heroic Strike
6) Overpower

9) Tough Jerky
0) Water

First Thing: Get some extra action bars. Press Escape/ Interface Options / Advanced Tab. At the top of this window are tick boxes for left and right bars. Tick them all. Whilst you're at it check that Quest Text is set to instant display.

Second thing: Move the food, drink etc onto another action bar.

Third Thing: Organise your buttons. Warriors have 3 stances: Battle, Defensive. Berzerker. These three stances have a lot of similar (analogous) spells between them. Some spells are available in All, or more than one stance; others have a similar function with a different name.
Revenge is similar to Overpower. It is triggered by the same conditions. Map Revenge in Defensive to the same button that you use for Battle. Rend is usable in all three stances, so map that to the same button across all stances.
Mocking Blow and Taunt are also analogous to each other, so you'll be mapping those together.
Sunder Armour is usable across all 3 stances but (maybe) only works with 1H weapons. Depending on how you use Bererker Stance (in 14 levels time) you will map Sunder across the same buttons.

You can slot in the rest, depending on how you like to use them. A common technique is to arrange the action bar in time order: Opening moves (Charge / Shoot / Auto-Attack to the left; your fighty moves in the middle, Execute at the end.

This isn't perfect, or even good, but it's a start. You will find problems with it: It'll be too unwieldly to work; You won't see any point in using X, Y or Z; You'll get a gamepad; You'll prefer to mouse. No worries, sort it out so you feel comfortable. This is your start.

You'll discover fun things like Shield Block, Heroic Strike and Cleave having different cooldowns to everything else over time, if you're clever, you'll build little sequences of attack moves so your fingers will automatically press the buttons, whilst your eyes are looking for trouble.