How to download Minecraft Resource Pack

First of all that what you need to install resource pack for minecraft is the resource pack itself, download a resource pack, you should get a .zip file. you can also download much resoucepack at http://resourcepack.net/

Installing Resource Pack

1. Download a resource pack, you should get a .zip file
2. Open the folder to which you downloaded the file
3. Copy the .zip file
4. Open Minecraft
5. Click on "Options", then "Resource Packs"
6. Choose "Open resource pack folder"
7. Paste the file into the resource folder in minecraft
8. Go back to Minecraft, the resource pack should now be listed and you can activate it by choosing it and hitting "Done"

Installing on another Operation System

Windows

1. Download a resource pack, you should get a .zip file
2. Open the folder, in which you downloaded the file
3. Copy the .zip file
4. Press ⊞ Windows + R then type in: %appdata%/.minecraft/resourcepacks
5. Paste the file into the directory
6. Open Minecraft
7. Go to "Options", then "Resource Packs"
8. The resource pack should now be listed and you can activate it by choosing it and hitting "Done".

Mac Os X

1. Download a resource pack of your choice
2. Do NOT unzip the resource pack just move the .zip file to minecraft's resource pack folder (Should be at ~/Library/Application Support/minecraft/resourcepacks)
3. Open up Minecraft and login
4. At the main menu select "Options", then "Resource Packs"
5. Now select your new resource pack and then select done

To access ~/Library/ on a Mac running Mac OS X 10.7 and above, switch to Finder, open the 'Go' Menu, and whilst holding down ⌥ Option, select 'Library'

Linux

1. Download a resource pack, you should get a .zip file
2. Open the folder to which you downloaded the file
3. Copy the .zip file
4. Type ~/.minecraft/resourcepacks/ in your file manager's address bar or in the console.
5. Paste the file into the directory
6. Open Minecraft
7. Go to "Options", then "Resource Packs"
8. The resource pack should now be listed and you can activate it by choosing it and hitting "Done".

And well done you have installed your resouce pack on your Minecraft.
Source : http://minecraft.gamepedia.com/Tutorials/Loading_a_resource_pack