The Clipboard on an Android device is an area of storage or memory to which small items can be saved. It is not an app and it cannot therefore be opened or directly accessed. Items saved to it are retrieved by long-pressing a blank area of a text field, say, and tapping Paste. Some phones will save only one item to Clipboard, which is overwritten and lost if a second item is saved. Other phones will save up to ten items, the desired one being selectable from a list before Pasting.
If you wish to take the functions of Clipboard to another level, enter 'Clipboard' in the Play Store search box and peruse the results.
More important items are best saved to less ephemeral storage than Clipboard.