im not to sure myself what they do..i think it helps for safe spawns..as in having to have them on your map no you do not you can still save upload n play on your map without them..but some people prefer you to use them. also you should try the search bar i think i saw an advanced respawn thread that covers respawn areas
http://www.forgehub.com/forum/forging-101/14285-advanced-guide-respawns.html The advanced guide to spawns AKA using respawn areas. It gets a little confusing toward the end of it but it explains spawns very well
I know what they do. you can set them to make it the original team spawn area, but I don't know how to make them. that link only shows how the spawns work, not to create them in forge
To create them, you first have to go into monitor mode and press start and select change gametype. Whatever gametype you pick will have the spawn areas that you place. They are then found under the 'spawn' category (i think)