I am not sure what exactly you are asking.
If you are asking for using net of your mobile to computer then there are different ways like connect your mobile using bluetooth and share net via nokia PC suite for Nokia mobiles.
If you are asking for making your mobile as a kind of router so that anyone can connect to it and share the internet of your mobile,then enable tethering and portable hotspot which will allow you to share your mobile device data connection Via USB,Wi-fi or bluetooth for android mobiles supporting this feature.
If you want to use the GPRS/3G/LTE internet capability of your mobile to give internet access to your computer then it would depend on the make/model of the phone you are using. As one post suggested, Nokia PC Suite is used for Nokia phones. As for androids and iOS phones, tethering is another option. This is basically connecting your computer to a mobile phone (as a wireless router/hotspot) through wi-fi and sharing the internet connection. Check your phone manual for tethering capability or you can also check for available apps that allows tethering.