Picking is handled automatically for a lot of things.
For instance, if you say "sprite is overlapping ground -> destroy sprite" then only the sprites that meet the condition are picked and destroyed.
If you know the unique ID of an object, you can pick it that way as well.
If there are no easy ways to pick like that, or you know you will have situations where some objects might meet similar criteria, you can make your own ways to pick with variables. Give each of your sprites a private variable, and make it unique. Then you can do "sprite.value('myvariable') equals whatever -> do something."