Assuming you would like a tutorial on how to install Minecraft Version 1.7.4:
First, make sure that you have Java installed on your computer. You can download it here if you need to: http://www.java.com/en/download/manual.jsp
Next, go to the Minecraft website and download the game client for 1.7.4: https://minecraft.net/download
Once the file has downloaded, open it up and run through the installation process - just follow the prompts and agree to the terms and conditions!
Once that's done, launch Minecraft and log in with your account details - or create a new account if you don't have one already. And that's it - you're ready to start playing Minecraft!