Yeah, read the wiki page but also, heres some quick answers.
1. The objective is whatever you set it to be. Personally I take on a pro-human role, basically healing humans and killing most undead on sight.
2. communicate by typing a message and clicking on 27.0 button, this broadcasts your message to the entire map. Don't abuse it because you might get ignored. You can also join a group, group chat is free and people will probably be willing to help you.
3. you have a chance of finding items whenever you enter and search a building. On the wiki page that Wanker linked go to the map and find the fort, head there and try find a GPS unit and some guns/ammo. You're going to have to search schools for a backpack and (If you're human) hospitals for meds.
4. if you die and want to be revived head to redemption street under the fort and call out on 27.0