Who are they ?
Whats the diffrent between Local Mod , Smod and GM ?
What can Local mod do ?

A local moderator is a moderator designated to one particular board. Their names can be seen at the bottom of the page.

All they can do is edit posts, threads, delete posts, threads, and move threads and posts.

Smods are supermoderators who handle the bans and read reports and the likes.

Gms are the Gamemasters who hold in-game events and act as ingame police.

Some local moderators are given the power to ban and infract on their assigned board, although this is rarely the case.

How to be one ?

You can apply when applications open.

You could also send a PM to an admin, but it doesn't do you much good, because the chances are slim if they aren't recruiting.

You can just apply when there are less local moderator in that board, as what above said.
But don't just apply because of the power you want, people can complain and admins may demote you.
Here, a full explanation about staffs.
http://forum.toribash.com/showthread.php?t=214880

Any requirement for that ?

Well, being a local moderator has to come with a passion for the section you are moderating. If you are moderating a section just to be a moderator, then you are nothing more then powerhungry.

Personally, I had quite the passion for discussion, and loved moderating it, which kept me motivated to do the job. Mind you, it is a VERY boring job sometimes, as you have to basically look at every new post and make sure that it is following the rules. Or at least thats what I did.

Requirements for local moderator are rather obvious. First, you must 'like' the section, and be fully aware of all of the rules of that section and the general forum rules. Second, You must be a level-headed individual(although some work around this, its harder to moderate if you rage at the slightest stupid mistake someone makes. You must have patience), and you must not have a biased bone in your body. You must be capable of enforcing those rules. Becoming one is rather simple, as local moderators do not have any critical responsibilities, and they are easily removed, if they screw up. You get the hang of moderating well over time, it is not just something that a couple people posting in rapid threads can teach you to do.

Well , how do Moderator Ban and Give Infraction ?

It's extremely unlikely that a local moderator will be trusted with those powers. The only one I know of that has been given them was Hyde due to his incredibly thorough moderation of Discussion. If you've actually been given the ability to do so, you should have a Mod CP (Moderator Control Panel; somewhat like User CP (User Control Panel)) you can do it from.