1. Extract the zip/rar/7z/etc. file to:
C:\Users\[your user]\appdata\roaming\.minecraft\saves
2. Make sure there isn't another folder inside your world folder (ex. If you downloaded "Awesome Save" make sure there is no "Awesome Save" folder inside that one. If there is, cut/copy it into the "saves" folder, and delete the empty folder.)
3. Play!
depends on the map some you just look some you play some you survive in etc.
You can make a custom map on minecraft with out a map editor by building or demolishing certain land features or you can use a seed by typing your seed in the bottom box on the "create new world" menu.
No it is a custom built map
escuse me but what?
You have to create a server and load the map to the server.
Of course you can. Minecraft has a folder with worlds in it in Application Support, so just put the map in.
SkyBlock is a great map.
-579322790607890076 is the seed and the map is custom
It depends on the map.
Minecraft Skyblock Survival is a custom map for Minecraft. In it, you are on a very small block of dirt with one tree and a chest with supplies in it. You can make a cobblestone generator and use the cobblestone to build and prosper.
nerdboy64's gun mod
There are most likely many. One of them is the lost custom map.
Yes, it is only a custom map. All custom maps are free, and you should never have to pay to play one.