Ais in the 3rd person

Bore da, I was wonder about “ais” I know prynais = I bought
Darllenaist = you read,
How would I use the 3rd person as in
he ran, she played, They ran, We spoke,

The usual ending is -odd: Prynodd e/hi lyfr, Darllennodd e/hi lyfr. The notable exception is 3rd person singular of “gwneud” → gwnaeth e/hi (also mynd → aeth and dod → daeth and probably something else I am missing off the top of my head)

Diolch Hendrik, so I can use the odd for he climbed = dringodd o
She wrote = Ysgrifennodd hi

Yes, perfect!