Do you have sync turned on? An easy way to check this is to long-press your home screen and add the Power Control widget. The two arrows in a circle are sync and that should be left on all the time. If that is on, also make sure that you are syncing gmail (you can also sync calendar and contacts with google's servers) via your phone settings.
If all that is on and you are still having to manually refresh gmail:
phone settings > applications > manage applications > menu > filter > all > Gmail storage > clear data > ignore scary dialog box and click OK
where would one find said " email check frequency"? im using the gmail app and i have to manually refresh it to get emails
The gmail app uses "push", meaning that you cannot set the frequency. It checks for email more or less immediately.