So,first thing's first- you need to install either Forge or Modloader (use this if forge has issues).I recommend using "force update" from the launcher beforehand to make sure that you have a vanilla .minecraft folder.
Here are the install instructions for them:
1.Press the Windows key+ R;
2.Write "%appdata%" and press enter;
3.From there go to Roaming\.minecraft\bin;
4.Right click minecraft.jar then select 7-zip>Open archive;
5.Delete the META-INF folder;
6.Paste the contents of the forge or modloader zip;
As for installing the mods,each one has a different way to install that can be found on the post/article of the mod on the site you got it from. For most of them you just need to move(move, not extract) the zip file in .minecraft\mods(do this if you can't find any instructions).Always backup your .minecraft!
If you need help with a specific mod just PM me or write here.