How do I close open apps on my new ipad

While closing apps is not really necessary and can be left in the background without any ill effects you can close them if required by swiping up from the bottom of the screen to the middle of the screen (on iPad's without a home button) or double clicking the home button to bring up the App switcher.

From there you can swipe each App up and off the screen to close it.

See here: link-> Close an app on your iPad - Apple Support

Open Safari tabs can be individually closed by tapping the small “x” icon at top-left of the open tab.

You can alternatively simultaneously close all open tabs using the tabs button (two overlapping squares) at top-right of the Safari window. Touch-and-hold the tabs button; an Action Menu will appear. From the Action Menu select Close All Tabs - highlighted in red text.

The iPad User Guide for iPadOS is also a rich source of information about your new iPad. Here are links to both the downloadable and online versions of the Guide:

‎iPad User Guide on Apple Books

iPad User Guide - Apple Support