If you have a mayor title or higher you can already claim your domains using the Domain and Settlement Selection portal found here

If you are gentry tier then purchasing land with EP won't be something that is available till exposition which is still a ways off.

You will be able to buy domains again in Settlers of Elyria event, which is expected to start somewhere soon.

SoE event

I have a mayoral title. I found the map, I'm not quite seeing where or how to claim on it though.. do I have to go into something specific?

Yes. So you should have selected a server if you want to select, then you look at that servers map by clicking on the corresponding letter.

Pick a kingdom to look at and a popup window should appear where you can click "Look Inside"

Do this again for a Duchy and a County and you will be able to see the settlements available in that specific County.

If you back out and select a different county, or duchy, or kingdom you can look around and see what is available to claim.

To claim you should simply have to select one of the settlements and then click the "Claim" button, but I would suggest looking around to find one you want first :D

Awesome thank you, I'll take a look and see what I can find!

Just a warning, once you choose a server your locked in, no ifs no buts.

Also, once you find a place to claim, try to contact the Count to let them know you'll be in their county or failing that, the duke or kingdom. It's a friendly way to proceed. :)