First of all, make sure that mobile internet is working properly. Go to Play Store, the icon of which you will find in the main menu. As you open it, a search bar/sign will appear on top right side of the screen.
Click on it, and search for an app capable of using your Android deice as a modem. An example is PdaNet. Write the app’s name, and the phone will come out with apps with this name.
Pick PdaNet 3.50 from the list. There will be a few others, but this is the most appropriate. If your mobile phone does not support this app, it means that you cannot turn it into a modem.
Others need to install it quickly. Click ‘Open’ to start the app, when ready. To make sure that the app is installed accurately, look for his icon in the main menu.
After downloading the app, you need to connect your mobile with PC through USB cable. Having done this, you need to click "USB Tether Mode" on your Android.
Those who are using Ice Cream Sandwich must know that as soon as you plug in the cord, the status bar indicates it. By tapping down the bar, you can make sure that the cable is connected properly.
When you click "USB Tether Mode", a warning message will appear on the screen with two options, ‘Yes. Let me download’ and ‘No. Already installed’. Since you have already installed the app, select the second option. This is the final step, and your device is now ready to be used as modem.