Examples might include:
This is one of the most common types of active check you will be asked to roll, though if you're trying to do something with more targeting, you may be asked for an Intelligence (Investigation) check instead. It's the difference between being vaguely aware of your surroundings in a small room, and actively looking for a hidden keyhole or trap door.
Clerics, Druids, and Rangers use Wisdom as their spellcasting ability.