You can, but you need the mod modloader. It allows you to run multiple mods at the same time.
You can use more than one mod if you use the mod "Mod loader". It allows more than 1.
Unplug your hard drive and put it in your computer and get mods for minecraft
No your have to wait for the mods to update which may take some time.
No
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.
Not without mods (modifications). Mods are extra files that you put into your minecraft.jar folder, which can change the game completely.
It requires mods. It is not possible in Vanilla.
No it might be that you have an out dated mod that crashes to game or that you do not have something like modloader (which you need for most mods). Also when downloading mods make sure they are for your current version of minecraft or it will defiantly crash.
Yes, the vast majority of Minecraft mods are free. I cannot safely say that all of them are, however I have not seen one that wasn't free. It would be illegal to try to sell a Minecraft mod. My suggestion is to visit the related links below for more mods!
Herobrine is not in Minecraft. This is just a running joke that've existed over the years. You can add him in with various mods though.
No, as long as you get it from the official website minecraft.net. BUT if you start installing mods there is a chance they could be a virus. So always get your mods from credited sources.
versions -> 1.6.1 -> 1.6.1 -> 1.6.1.jar -> there you put your files
you go download it then run it and put it in your mods folder if this does not work then read the installation instructions because this could be out of date