Most screens have menu/s that can be accessed by a "right click" on your mouse while "anchored" in a cell.  The below shows the "Right-Click" menu when anchored in the BudgetID cell on  Manage Budget Accounts.

To use the functions available on the menu, click on the function.  For example, below "Check All" resulted in all the rows being checked.

The menu also lists the "Short-Cut Keys" for the available functions.  These functions can be used without using the "Right-Click" menu.

For example if you wished to "Uncheck All" you could do so by holding down the "Ctrl" and the "U" keys together on your keyboard.

Please see related article:

How Do I Right-Click on an Apple (Mac) Computer