i have my ipad connected to the computer, why dosent it update automatically?

This support page outlines the available methods of updating you iPad:

Update your iPhone, iPad or iPod touch – Apple Support

The tags appended to your post suggest that you have an iPad2. As such, your iPad might already have been updated to the most recent version of iOS that it can support...

iPad2 cannot be updated beyond iOS 9.3.5 (WiFi Only models) or iOS 9.3.6 (WiFi & Cellular). Apple ended update support for this model in September 2016. iPad2 cannot be updated to iOS 10, or later versions, as the internal hardware does not meet the minimum technical requirements for new versions of iOS/iPadOS.

Many App Developers have also dropped support for older devices and iOS versions preceding iOS11/12/13 - and have withdrawn older versions of their Apps from the Apple App Store, now limiting utility and usefulness of older devices. 

If Apps that you need to use now have higher minimum iOS-version requirements, your only option is to replace your iPad with newer model. Even the entry-level iPad7 model supports current iPadOS 13.x and soon to be released iPadOS14 - and has hardware specifications and capabilities that will vastly outperform your old iPad.

I hope this information is helpful - if only in clearly stating the limitations your iPad and your potential options.

because you have to tell it to, there are instructions to follow on screen