You'll be fine as a new tank. Some general advice, though: 1. Say you're new. People in FF14 are generally pretty tolerant of people that are new, and might even offer you some more advice.

1. Go one group at a time. Pull with tomahawk, move back a little bit if needed to make it safe so that you don't pull another group, and then use overpower 2-3 times to establish aggro. Pick a target (usually the one you used the tomahawk on, but if the DPS are attacking something else for some reason, switch to that) and use your combos on them.

You should be good for the whole pull with this, but if it starts going longer or your DPS are splitting who they are attacking, throw out another overpower or two.

Also, don't be shy with your cooldowns (which I think is just foresight at this point?). Use them every time you can on a pull, as soon as things start attacking you, and don't stack them once you get more than one unless you are REALLY getting beat on (usually because you pulled more than you meant to or a dps aggro'd another pack accidentally or whatever) and the healer is struggling.