I'm confused about combat; how can I hope to hit anything?
Me and my friends are pretty new to D&D and are likely getting the majority of the rules wrong. I believe I understand AC: an AC of 16 means you must roll a die (+modifier) of 16 or greater to deal damage, and anything over that AC is taken as hitpoint damage?
What I was wondering was, at level 1, I believe I have a d10 halberd and a +4 strength modifier. However, the guards we're fighting have an AC of 16, making it completely impossible to even get past their AC. So we played it as if we could group attack, i.e. add up all our attack scores then remove whatever was excess of the AC from HP. Pretty sure we're playing some rules wrong, could anybody shed some light on the subject?
Not sure which version of D&D I'm using. It's the free pdf version released in August: http://media.wizards.com/2014/downloads/dnd/PlayerDnDBasicRules_v0.2.pdf
I have read the armour class section of the rulebook. Is it perhaps that first you roll a d20 (+modififers) to see if you beat armour class, then you do a damage roll?
Let's break this down a little bit using the Basic Rules you have available.
To make an attack roll, roll a d20 and add the appropriate modifiers. If the total of the roll plus modifiers equals or exceeds the target’s Armor Class (AC), the attack hits.
Pretty straight forward. You roll a D20 and add modifiers, in your case +4 for your Strength as well as your proficiency bonus if your proficient at using a halberd, and that result determines whether or not you actually hit the target. Now the DM might or might not tell you straight up what the AC for an enemy is, but if you're paying attention you can figure it out by remembering what rolls hit or miss and extrapolate from there.
If it hits then you roll damage.
Each weapon, spell, and harmful monster ability specifies the damage it deals. You roll the damage die or dice, add any modifiers, and apply the damage to your target. Magic weapons, special abilities, and other factors can grant a bonus to damage. When attacking with a weapon, you add your ability modifier—the same modifier used for the attack roll— to the damage.
In the case of a Halberd, the damage die it talks about is your aforementioned D10. So if your D20 + Strength modifier + Proficiency attack roll is at least equal to the target's AC, you then do your damage roll. For your damage roll, you roll a D10 and add your +4 Strength modifier and that is how much damage the target takes (you don't need to worry about their AC for the damage roll).
This all explained pretty clearly in the rules, but I can see how confusion might stick if you are new to it all and are starting from some misconceptions.
Most importantly, the d10 is used for damage when fighting with a halberd, but you always roll a d20 to see if you hit, no matter what the weapon. (A d20 is used for most checks to see if something succeeds — attacks, saves, and ability and skill checks.) So, you can hit that AC of 16 with a +4 modifier — you just need a 12 or better. And since you add in your proficiency modifier when you are proficient with the weapon, that's another +2, so really you only need a 10 or better.
If you hit, use the d10 and modifiers to determine damage. Beating the target with the to hit die by more than needed doesn't do anything for you, unless you roll a "natural 20" — a roll of 20 on the die without modifiers. This is a critical hit and does extra damage.
Also, a natural 20 always hits in an attack even if the AC is ridiculously high. A natural 1 always misses. (Note that this is just for attacks, not other checks or saving throws.)
Your idea of having everyone work together to hit a difficult target isn't bad either, although it doesn't work that way. Look at the "Help" action (on page 72 of the v2 basic rules, or page 192 of the Player's Handbook). This has worked differently in different editions, but in 5e, it means you can use your action to feint, distract the target, or something similar, granting advantage to an ally who attacks the same target before the next turn. This drastically affects your chances of succeeding and of getting a high-damage critical hit. (See page 4 in the basic rules for more on advantage.)
Bonus tip! Generally, to speed things up, you roll all of the dice at once — the d20 to attack (and the second d20 if you have advantage or disadvantage), and the d10 (or whatever) for damage. Then, of course, if you miss, you just ignore the damage die.
It is exactly as you're saying in your last paragraph: you first roll a d20 plus modifiers to see if you hit or not, then if you hit you roll for damage, a d10 in your case plus a different set of modifiers.
From page 9, Weapons:
When you make an attack with a weapon, you roll a d20 and add your proficiency bonus (but only if you are proficient with the weapon) and the appropriate ability modifier.
Attack Rolls, on page 73, further details the process.
Simply put, to attack you roll 1 20 sided dice (1d20), you add 4 extra score on top of your rolled score, and now you have your attack score.
For example you rolled a d20, and it turns to be 17, now you put 4 to make it 21. Your enemy's AC is 16, so you hit him. Now roll 1d10 plus your damage modifier.
Good luck !
If your strength is an 18 and you have a +4 modifier than you will have a +6 (+2 proficiency bonus at level 1) to roll the dice to hit your target. With an AC of 16 this means you need a 10 or higher on a d20 to hit. This means you have a 50% chance to hit your target at level 1.
After figuring out you have a hit, you then get to roll your 1d10 with a +4. So you will do somehwere between 5 and 14 damage, when you hit, which will be about 50% of the time, with a target of AC 16.
So it should not be nearly impossible to hit, unless you are fighting against a creature with an AC of 25 which will only give you a 10% chance to hit, or an AC of 26+ which will give you only a 5% chance to hit.
Attack roll is separate from damage. When AC is beaten, meaning 1d20+Ability Modifier+Proficiency+Miscellaneous Modifiers (EG;Fighting style). If all that equals above 16, you hit. You obviously total modifiers for convenience.
When you DO break AC, it doesn't matter if you roll 30. You do not add the roll over number to damage, although....it makes sense, honestly. It justifies that hard hit. ANYWAY, you disregard the roll after you know it breaks 16 You roll damage dice after breaking AC.