The third eye lid, also called the nictitating membrane, will protrude over the bottom inner corner of the eye. In the pictures above, notice that the third eyelid also protrudes when you pull up the upper eyelid. The 3rd eyelid is usually a pale pink or white color and has thin blood vessels on its surface. When you pull the lower lid down it pulls way from the eyeball creating a pouch that is lined by pink conjunctiva. This pouch is where eye medications are placed.
Ointments stay in the eye longer than drops so are usually applied less often.
Your veterinarian will prescribe specific medications for specific conditions. Use the thumb of the hand holding the head to pull down the lower eye lid to create a pouch. Hold the ointment tube in your right hand, with the tip a few millimeters away from the eye, not touching the eye, squeeze a small ribbon of ointment into the pouch. Hold the head and pull down the lower eyelid as described for placing ointments in the eye. Drop the prescribed number of drops into the pouch without the tip of the bottle touching the eye.