I've heard you could but I'm not really sure so sorry if this wasn't any help
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.
It depends on the map.
SkyBlock is a great map.
-579322790607890076 is the seed and the map is custom
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
Google: Minecraft Skin CreatorMake your skinDownloadGo to Minecraft ProfileUpload skin
There are most likely many. One of them is the lost custom map.