Just like you mod any game. Sometime the game may have its own modding tools, or sometimes you just have to take the game files and edit (MODify) them.
No. You have to buy Half-Life 2 also.
Depends on what you are looking for. If you torrented Garrys Mod ( Illegal Copy ) then you must mount the .ISO file. Then crack and istall. But, if you bought the copy of Garry's Mod off of steam, then directly after you purchase the game it will show up in your library and start downloading
I mod alll da games
ESET.Smart.Security.5
No, it isn't illegal to mod any game unless it is online or it is a mod to play burnt games.
you can mod COD games
Garry's mod is a tool not worth mentioning, why would you mod sprites when garry's mod works on games with high res models?
Yes, you can. It's illegal to do so though, except if you already own the game and intend to use the torrented version as backup, I believe. But it's certainly possible.
Garry's Mod is only for Valve-released games, so no.
Don't do it. It is ILLEGAL!
Stanky leg
Yes