if it is just minor secretions, you can probably let it go.  he probably
just got something in his eye.  If it doesn't clear up soon, gets worse, or
the kitty displays other symptoms, you should get him to a vet.

You can use pure saline to flush out the eye, much like you would add saline
to your own eye if you got something in it.  but I wouldn't go messing
around too much with eyes.  they are very delicate.