Attacking with ze longbow:
So let's crunch down Kiramor, the level 4 ranger/2 rogue (total level 6)
He has two ranged attacks, namely:
Ranged +1 longbow +10 (1d8+1/x3)
Ranged +1 longbow +8/+8 (1d8+1/x3)
The first part, that is, every number and name after "Ranged" and till (and including) the name of the weapon, is the full name of the weapon. In this case, that is +1 longbow. The longbow part means it's a longbow, the +1 part means it's a magical attuned weapon. It's magically enhanced to hit more often (giving a +1 on attack roles) and do more damage (giving +1 on damage roles). Some weapons give higher bonuses, like a +3 longsword gives +3 on attack and damage roles. Other weapons might have special properties, like a +1 flaming scimitar. It does not only have the +1 magical enhancement bonus, but also has the flaming property, which makes it deal 1d6 extra fire damage. The magical properties and its costs are well described on page 468 of the core rule book. Masterwork weapons (have "mwk" on the place where "+1" would be, just like Kiramor's melee rapier), give the +1 bonus on attack, but not on damage. This bonus does not stack with the magical bonus, since all magical weapons are masterwork to begin with!
Now comes a confusing part. We have the same weapon (a +1 longbow) with two different attack modes? What are does +10 and +8/+8 for? Well, as you might know, you need to roll a d20 to see if you hit an opponent. You have to beat the opponents Armor Class (AC in short) to hit. When you roll the d20, you may add your attack bonus to your roll. For a ranged attack that is Base Attack Bonus (BAB) + Dex + other bonusses. Let's look at Kiramor:
BAB = +5
Dex = +4
Other bonusses = +1 (The +1 of the magical longbow!)
Total = +10.
That makes sense with what's written with the first attack, right? So he can shoot one arrow with his +1 longbow, with an attack bonus of +10 and dealing 1d8+1 damage, triple on critical.
The second attack mode, is using his special feat, Rapid Shot. Look it up under feats what it does precisely, but it means that at a full-round attack, the owner of the feat may fire 1 extra arrow at his highest attack bonus, but takes a -2 penalty on all attacks.
So the slash means a new attack. His first attack (his normal arrow) would be at +10, but Rapid Shot lowers this with 2 to +8. His second attack after the slash also uses his highest bonus (+10), but is also lowered by 2 to +8. Another mystery solved. Two attacks with his +1 longbow, with an attack bonus of +8 each and dealing 1d8+1 damage each, triple on critical.
Note that when you have a BAB of +6, you naturally get a new attack, without the use of feats, on full round attacks. Look for the Ranger class table on page 66 for a moment. See that his BAB at level 6 is +6/+1? This means that in a full-round attack, he can do two attacks: The first uses BAB +6, the second uses BAB +1. So first attacks always have a bigger chance to hit.
Some feats may give you extra attacks, like two weapon fighting of the captain in the GM guide. These have slight different rules. For example, the weapon you wield in your off hand gives only half your Str bonus on attacks. That's why the captains second set of attacks deal 1 less damage each.
HD and hp
Hit Dice (HD) is the number of hp-dice that are rolled for this character. Back to Kiramor, his hp says:
hp 39 (4d10+2d8+6)
What does it mean? Well, the numbers before the "d", in this case 4 and 2, are the amount of times that that specific dice is rolled for hp. So he rolled 4 10-sided dice and 2 8-sided dice for hp. Why? Well he has 4 levels in ranger, and each level in ranger gives you one roll on the d10 for hp. He also has 2 levels in rogue, which gives him 1 roll on the d6 per level in rogue. So 4d10+2d6. That would be a minimum total of 6 (roll 1 each time) or a maximum of 52 (roll 4x10 and 2x6). Now as you may know, constitution gives you more hp. The rule is that for each HD you posses, you get your Con modifier as bonus hp. So Kiramor has 12 con, a modifier of +1. This means he gets 1x 6(number of HD) bonus hp, for a total of 6. That explains the +6!
How did they get to the final hp? Well they don't actually roll, but take the average: 4x5.5 (4d10) + 2x4.5(2d8) +6 = 37. They just gave him +2 hp because the felt like it, I guess. Thats a magical GM trick.
Notice that for player races with class levels, like humans, elves and dwarves, the HD is equal to your level. After all, you only roll a hit dice when you level up! For other monsters, HD might rise more steeply to match the players level. For example, an animal which is a normal challenge for a level 6 party (CR 6), has roughly 9 HD. This is so, because when a player gains a new HD and a new level, he also gets new abilities and better scores. Animals have worse "level ups" and thus need more to be equally challenging.
Hope this makes sense!