Well I hope this topic will help you, it would help me
First is Windows installation.
1.Download Forge the latest version 1.5.2 and make sure you MC is 1.5.2
3.Now hit the "Start" button on your Desktop and type in the search bar "%appdata%"
4.Double-click "Roaming" then double-click "minecraft"
5. Open your bin folder
6. Right-click you minecraft.jar and open-with WinRAR, put that window aside.
7.Open Forge with WinRAR and drag all of its components into the minecraft.jar.
8.Now run MC once to the Title Screen to generate a "mods" and "coremods folder"
9.Then go back to the mincraft folder and you will see a mods folder thats where you will place most mods,
some may need to go in coremods the author of the mod should tell you. Enjoy
1.Download all the same things but you dont need WinRAR.
2.Go to Users/Application Support/minecraft/bin
3.Use the Unarchiver tool on the minecraft.jar
4.name the .jar you unarchived minecraft old.jar
5. name the folder you got minecraft.jar
6.Copy the forge components in its folder to the minecraft.jar
7.hit apply to all and replace
8. run it do genrate mods and coremods folder