forgot my ipad passcode, how do I reset it?

Bad news first, there's no way to get in without erasing it, unless you changed the passcode in the last 72 hours (newer iPadOS lets you use the old one for a while). On a recent version, keep entering wrong codes until it says iPad Unavailable, then tap Forgot Passcode? in the corner and erase it with your Apple ID password. On older versions you have to put it in recovery mode, plug into a computer and Restore with Finder, iTunes or the Apple Devices app. The button combo depends on whether it has a Home button. Either way you need the Apple ID password afterwards because of Activation Lock, so sort that out first if you've forgotten that too. Your stuff comes back from iCloud backup if you had one.