This varies by modification. Read the website of the mod or the readme that came with it.
Buy Garry's mod 10 off of steam.
technically yes, there were a few updates it is still called Garrys mod 10 though
Garry's Mod 10
no because garrys mod requires that you have a game that uses the source engine
Garry's Mod has now updated and includes all features of 13 Beta
Garry's mod tornado
Steam
yes
yes, take a load of red containers ararnge them in a huge cube and make one in the centre of it all empty, sit in it and set off a nuke on top of it, you won't survive, but the building will.
You Do Not Get Garrys Mod Serials, You Buy it Off Of Steam Which can be found at steampowered.com its usually about 21 United States Dollars
E
no