What should I do to get Internet on my Iphone 4?

Every time I try to use Internet on my Iphone it shows 'Could not activate cellular data network. You are not subscribed to a cellular data service' icon.
I'm new with all those apple things, so a little help won't hurt.

You need to have a data plan for that phone to use cellular data. You can also go into settings app and log onto Wi-Fi if some is available.

Go to Settings and surf through each option and when you come acros a sub-option called "Mobile Data" make sure its on the 'On' position. If it didn't work after word, contact you Network Service provider and inquire about your contract or payG internet settings, they'll tell you how to set up it coz internet setting depent on the network provider.