If you have a plan with loads of included data and you'd like to share it with another device, like a laptop or tablet, you have a couple of options.
WiFi Hotspot: All new smartphone have a function built in which turns them into WiFi modem that you can then connect your laptop too.
You can find this in the Settings menu on your phone under 'Personal Hotspot' on your iPhone or 'Connections' on your Android phone. Just setup a network name and password and you're away.
Data sharing plans: the major telcos now have data sharing or family plans, which let you connect multiple accounts onto the same bill and share all of the data included with each account. You can put a data sharing SIM card directly into a tablet, but you'll need a USB modem to use these feature with a laptop.
Note: because webpages are compressed when viewed on mobile phones, you will use a lot more data visiting the same pages on a laptop - and will use more data as a result. If you do share your data, be sure to keep an eye on your data limits.