Skyrim Mods Installation?

"When you download mods, do they just automaticly turn on or do you have to do that? and How?"

If u use a mod manager such as Nexus Mod Manager or Steam Workshop, the mods are automatically unpacked and placed in your Skyrim/data folder. U may need to engage the Skyrim launcher and choose the "data files" tab and tick the boxes next to the mod names to enable them in-game.

"When a mod is in your game, (like an armor) will it be in your inventory or will you have to buy it at a shop somewhere on the grid??"

This all depends on the mod. In our clothing mod, we created a special vendor who sells the clothing items to the player character. Some mods may just store them in a chest somewhere. U will have to read the description and/or readme which is associated with the mod.

"And last one, if you download a shape or face, how do you put it on your character?"

Again, the description page or the readme included with the mod will give detailled instructions on how to access the mod in-game. Generally, retexturing mods will be automatically applied as the .dds texture file will still have the same name as the vanilla texture file, but will be edited to reflect the new look.

Just make sure u read the description/instructions/readme of each mod u are wanting to install. The comments section (on Nexus) will also be informative as to whether the mod is compatible with various other mods, if people have encountered bugs, etc.