How do you play wow for free if i want to play it with my friends

First off, it's not possible to play World of Warcraft beyond the limits of a trial version without having an active subscription. This means you will have to pay for it.

If your friends are playing on a live server, the only option to have contact with them in-game would be through a Trial version, which is available from the wow website. You won't be able to do much, but you can chat with them.

Other than that the only thing I could come up with is trying to see if there are online sweepstakes or the like where you can win game time cards (Blizzard itself has a few promotions like that) which would allow you to extend your subscription.