How paste from clipboard

Usually, from my experience with iPad Mini and two iPhone models (with three different iOS)

you can copy an item (such as image) by holding down on awhile after touching it. ~ A tiny

window appears in an most iOS with choices on what may be done with the item. And text

selection to copy is more tedious, depending on touch dexterity, product & iOS user interface.

Copy is one of the choices. To Paste there is an icon on edge of screen of tablet or shape; is

Clipboard, and where item previously copied to, is retrieved. In most instances by touching it.

Also I've found in some applications, you can touch and hold to get a copied item to paste.

These vary somewhat between iOS; if one is using by Messages for Mac, options are better.

Your mileage may vary. And there is a good free app manual for iOS11 from Apple. This does

cover most hardware application of iOS. A list of suited products appears in iOS11 app.