The verb caer (conjugation) means "to fall". It is irregular in the present tense. The ending er changes to go in the (yo) form (first person singular). Also, a changes to ai in the yo form of the verb.
(you guys fall)
(you all/they fall)
Sentences using caer in the present tense
Yo caigo de rodillas.
I fall on my knees.
Ellos caen de cansancio.
They are (falling) so tired.
Note: There is a special use for this verb: "caer bien" means "to like" and "caer mal" means "to dislike".