That's not much information to go on.
However, my first guess is to check you APN settings (Access Point Names). These will be in the mobile/cellular data settings. Make sure these are correct for your network - you should be able to find the settings for your carrier on the web somewhere, either on your carrier's website or else a search will generally find them. These not being set, or not being set correctly, is the commonest reason people can't get the internet on any phone.