If you are playing on multi-player, you will see other players, but on single-player, there are no other people.
yes, you can see and interact with their avatars.
Yes you can you can even host your own server on your PC and just have your friends on it. Or you can go and find other peoples server and play with people across the world!
You can open a LAN server if they are within your household, or you can join a server.
Minecraft seeds can be found on the Minecraft forum. See the related link below.
yes
You need a premium Minecraft account to play online with other people.
They can get into your ender chest, but they will not be able to see your items. Contents of Ender chests are private for all players.
Minecraft is not see through?
You select multiplayer and you may see servers. If you don't and your friend knows some or you know some of them, you go to direct connect and type it in.
Search Yahoo/Google/Bing for "Minecraft Mods". Read the instructions on what and how to install them and see if they are compatible with the other mods your going to put in.
They can if the developers see it and see it as a good idea.
Check the forums for your other mods to see what mods they are compatible with.
u dont other people do that 4 u
Yes, see the related link below for Minecraft's official site.