New to 4E

[Jimbob]

Ok people im new to 4E but have been playing 3.5 since the start.
So my quick question is. I am going to play a halfling rogue with an 18 dex.
Now my basic weapon attack is 4 (3 for dagger prof and 1 for str).
But if I want to make a dex attack what modifiers do I use? Would I have a dex attack of 7 (4 dex, 3 dagger prof) or just a straight 4 for my dex? And does this increase with things like weapon focus and level bonus?

[tcrudisi]

Suggestion: if you are using point buy, make that Dex 20. Dexterity is all-important for a Rogue. It determines your best skills, your initiative, your ability to hit, your damage, and your AC and Reflex. It's one of the few classes that wants to start with a 20 pretty much all the time.

If you are talking about a melee basic attack (MBA), yes you use Strength. That's a bit of an illusion, though. You really shouldn't be using your MBA that often. Only when the monster incurs an opportunity attack (OA) from you. But, if you really want to make it better, take the Melee Training feat. It will allow you to use Dexterity instead of Strength for your MBA's. If you are level 1, I'd wait until level 2 -- why? Well, it lets you see how often the DM actually incurs OA's from you. If never, then you know you don't need that feat. (Exception: You have a Warlord in the party. If so, I would take this feat at level 1.)

Weapon Focus increases your damage, not your attack bonus.

If you use a ranged basic attack, that is based on Dexterity. In that case, you would do Dex bonus + weapon proficiency + 1/2 level + weapon enhancement + any other bonuses. In this case, at level 1 and using a non-magical dagger? 4 + 3 + 0 (always round down, 1/2 of 1 is 0) + 0 (not magical) + 1 (Rogue Weapon Talent) = +8 to hit.

At level 5, assuming you are using a +2 dagger?
4 (dex) + 3 (wpn prof) + 2 (half level) + 2 (enhancement bonus) + 1 (rogue weapon talent) = +12 to hit.

Finally, I'm going to take a guess that you are looking at basic attacks and not your actual powers. As a rogue, all your powers will use Dex to attack with in melee combat. Look at something like Sly Flourish. It uses Dex to attack with and do damage (plus Cha, actually, if I'm remembering the power correctly off-hand). Unless you are a Brutal Scoundrel, Str is not important to you under most circumstances.

/edit - Also, find out if you are using the errata. If so, Rogues got a huge upgrade. Your sneak attack is usable once a turn rather than once a round. This makes a big difference.

[Sol]

Attack bonuses are:
The stat modifier of the stat the attack calls for
Weapon proficiency bonus if you are proficient and the attack has the weapon keyword (all rogue attacks do as far as I know, but if your racial power is an attack, it will not, so won't get this bonus.)
Half your level (rounded down)
Enhancement bonus if you have a magic weapon
Feat bonus from an expertise feat (much better than previous editions)

There are a few less common ways to increase it further but that's a good start. Also try to learn all of the ways to gain combat advantage against your targets, to gain an additional +2 to hit (or +3 with the nimble blade feat) and to deal your sneak attack damage.

[Jimbob]

cheers guys that clears it up for me