First of all, you must download it. Next (if you want to get mods) you must open "Run" (for Windows) and search app data, it will get you a option of 3 things, but open "Roaming". Then open .minecraft, open bin, then you'll see a java file, minecraft, right click it and scroll over open with, and open with WinRAR Archiver. Then open the mod file with WinRAR Archiver and drag the contents into the jar file.