Installing resource packs (or prior to 1.6 texture packs) manually is not always an easy process, so we've created this guide to help you along the way. For an automatic solution to resource pack installation, we encourage you to give the Twitch App a try.
Note: This guide does not show how to install mods or modpacks. If you wish to install mods or modpacks in your SP game please use the Twitch App to assist in installing them.
You do not need to exit Minecraft. You can install resource packs while being logged into the game.
Note: This guide is focused on Minecraft 1.6+ and the Resource Packs for 1.6+. So make sure you have an updated Resource Pack.
Downloading the AddOn
Make a folder on your desktop called My Resource Pack
Download the Minecraft Resource Pack you want to install and save the compressed files (.zip, .rar, etc.) to this folder.
Usually when you download a file it will give you a popup asking if you want to open it or download it. You want to download it. If you are not given this options try right clicking on the link and Save As... or Save Target As.
Extracting the AddOn
Unlike AddOns for other games you do not need to extract the Resource Pack.
Verify your Minecraft Installation Path
This is the location of where you have installed Minecraft to. By default it is:
*ACCTNAME - Will be whatever your Windows User Account name is.
However, some people have their hard drive partitioned or have multiple drives so Minecraft may be installed on a different pathing.
You can also locate this are through Minecraft while logged in. Click ESC.
Install the Resource Packs
Open your Minecraft folder that you found above.
Go into the resourcepacks folder.
Open the My Resource Pack folder and move the compressed files (example SixtyGig_Alpha_64x_MC17.zip) in your My Resource Pack folder into the resourcepacks folder.
Making sure Resource Packs are Installed
Start Minecraft and log in.
Before choosing Single or Multiplayer select Options... > Resource Packs
You will then need to make the Resource Pack you want active. Hover over it in the left column until you see an arrow pointing right. Click the arrow.
You can have more than one Resource Pack active at a time. The very top one is your main. If any resources are missing from that pack it will use the one below it. If any are missing from those two it will use the one below that and so on.
If you are not seeing your Resource Pack click on the Open resource pack folder and double check to make sure you copied over the Resource Pack file to the correct folder.
If you continue to have issues you might want to consider giving the Twitch App a try.
Note: Some Resource Packs, like the one in the guide, requires MCPatcher for it to display properly in-game. For further assistance with that, check out MCPatcher's Post on the MinecraftForums.net.