The fact that your computer has 3G capabilities means that you can insert a SIM card into it and use that to connect to the Internet through 3G network. Before you can use this service, check the User Manual that came with your computer. By doing this, you can find out more about how to insert / use the 3G capabilities of your PC. Also, you should visit the following website, and properly chose your OS. by doing this, all the appropriate drivers will be installed. If you followed all the steps provided, you probably already are connected to the Internet through a 3G netwrok.
