How do i restrict the forum to members only?

It's in the permissions for each forum. For every forum you create or have created, you have to change the permissions from All, to Members.

Go to admin panel=>Forums=>Permissions=>Forum permissions control and click on a forum.Click the "Advanced mode" button at the bottom of the screen(if you don't see it that means you are already using advanced mode). Now uncheck all the boxes(View the Forum,Read the Topics,Reply a message etc.) for Guest then click the save button. Repeat this for every forum that you have.

thanks, i thought there was a quicker way

Nope sorry there isn't. I usually just click that drop down menu at the top, where the choices are All, Members, Admins. Because that usually will check and uncheck all the ones you need to restrict guests, so you don't have to click each box individually.

But you might have to do some individual check marks using the Advanced like Luky suggested in order to give your mods the rights you want them to have. But you would need to do that anyway, regardless to whether or not, it was set to guests or members.

Happy clicking! hehehe