The iPad1 is obsolete. You will not find any compatible Apps in the Apple App Store; if the iPad is reset, any Apps already installed will be lost.
The iPad1 cannot be updated beyond iOS 5.1.1 - this being the final version of iOS for the original iPad.
For information, here is a list of the highest version of iOS supported by the older models of iPad (for simplicity - “generations” are shortened to a number) that are restricted in their ability to be updated:
iPad1 - iOS 5.1.1
iPad2, iPad3 and iPad mini1 - iOS 9.3.5 (WiFi Only models), iOS 9.3.6 (WiFi & Cellular)
iPad4 - iOS 10.3.3 (WiFi Only), iOS 10.3.4 (WiFi & Cellular)
iPad Air1, iPad mini2 and iPad mini3 - iOS 12.5.5
Newer models, not appearing in this list, are all able to be updated to the current version, iPadOS 15.2.1.
Regardless of the iPad model, if you are preparing the iPad for a new user - or for disposal - you should follow this process:
What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support