As Kirrotu said, modding is not plug-and-play super simple. Mod capability is simplified in Bethesda games though.
1. Open steam, right-click The Elder Scrolls Skyrim on the list on the side.
2. Choose Properties
3. Local files --> Browse local files
4. Create a shortcut to this place. It'll be useful.
In there is a Data folder, which is where the main game files, DLCs and mods go. When you get a mod, you copy the files for it (most mod authors will include a readme.txt. READ THIS, it will tell you anything you need to know about installing and incompatabilities) into there. Look for the .esp file, copy that and any other files with it into your data folder.
A program named BOSS can help with organizing your load order.
Now, a few things to remember:
1) Backup. Badly-written mods can cause problems with save files.
2) When you uninstall (delete) a mod, if you've saved the game with that mod active, it may cause issues if you load that save. For example, If you have 35 saves, install a script-heavy mod, load up save #35 and play for a bit with that mod, then save in slot #36, you may have issues with save 36 if you then uninstall the mod. Save #35 will be fine.
3) Be careful with .exe installers. It may seem quick and easy, but it could be malware or something (i believe somebody tried this not too long ago, posing as the author of popular mods and handing out malware). If a mod download has an .exe, only use it after looking at the comments, and seeing if it is a reputable modder.
The Nexus Mod Manager can help with simplifying installation, although I would suggest you do a little research into how to install mods and what that entails. Knowing what you're doing is a good thing.