Pit = general admission (not a designated seat, but GA pit will be in the front right up by the stage. If you can stand just fine for several hours, I'd say this is a good thing! :)
Will call means that you will pick up your tickets the day of the show at the venue. There will be a "Will call" window or table in the venue, typically near the ticket/box office. Bring your ID and the credit card you used for the transaction to verify your identity. You may only need your ID, but always a good idea to have the payment source as well.
Have fun at the show and come back to give us a review about it!