You can either get own one or get white listed and play on some one elses server. Some servers have survival mode enabled some dont. Alot of private servers have different texture packs and hacks and stuff.I'm not sure how the server thing works. I have yet to actually play on one. Just been doing my own thing with single player.
there are spiders and zombies and skeletons and creepers. You build to protect yourself from them. You can playin peaceful mode too which doesnt have any of those and just allows you to build and mine and build and mine and create stuff. And yes you can create machines too. furances and rollercoasters. On the server i play on the quickest way to get around is the mine cart track which is conneceted to all thes bases. There are 4 of them on this server since there are only 4 us on it.I don't even get what this thing is. What is the objective? What's "survival" mode?