This is an oft asked question and plenty of threads/posts already exist on the topic - try some searching and for starters, simply type in 'deleting photos' in the search box (left upper corner on the Forum home page).
But to get you started, take a look at THIS THREAD - good luck and please post back if this thread or your searched results still leave you w/ questions.
And if not already done, please obtain the iPad User Manual and read the appropriate chapter!
There is lots of good advice and info on here plus plenty of members all too willing to help with any problems.
Remember, search is your friend. If you can't find the answer you need and you post a question then give as much info as you can to help members help you i.e. iPad 1 or 2, iOS version and name of app if the problem is with a specific app........and please don't forget to read the rules http://www.ipadforums.net/forum-rules-help-info/2119-forum-rules-everybody-please-read.html
You can download the manual for your iPad here http://support.apple.com/manuals/ and in iBooks search for "iPad user guide for" and you will find free comprehensive manuals for both iOS 4 and 5.
If you have other Apple products or are interested in other Apple kit then why not join our sister forum too at http://www.appleforums.net/