Hi Horselover!
Bedding is the stuff on the bottom of the piggies cage that they walk on. It should be something absorbant (for the pee). You can either use normal "loose" bedding, e.g. carefresh, megazorb or aspen. Do not use sawdust, pine or cedar shavings. (Kiln dired pine is ok but can be hard to find). The alternative is the fleece method - check out this thread:
http://www.guineapigcages.com/forum/...ect-study.html
Piggies need grass hay (eg timothy hay) available to eat at all times - it is vital for proper digestion, fibre, wearing down teeth etc. Most guinea pigs also like running through and hiding in hay.
It is up to you how you present their hay. You can either just put it loose on the floor of the cage so they can run through it (although it will get peed on) or use a hay rack.
You're right it is dangerous for piggies to fall, so second levels and ramps must be made safe. Most people put grid walls around their upper levels to stop the piggies jumping off, and ramps should also have sides to prevent them falling or slipping off. The ramp should also have enough traction for them to grip properly.
Finally, please be aware that guinea pigs are a social species so you should adopt more than one.
Hope this helps