So with canu (sing):
mi wnes i ganu I sang
mi wnest ti ganu you sang (singular familiar)
mi wnaeth o/hi ganu he/she sang
mi wnaethon ni ganu we sang
mi wnaethoch chi ganu you sang (plural or polite or both!)
mi wnaethon nhw ganu they sang
canais i I sang
canaist ti you sang (singular familiar)
canodd e/hi he/she sang
canon ni we sang
canoch chi you sang (plural or polite or both!)
canon nhw they sang
But unlike English "I did look at the car", which is emphatic, "Mi wnes i edrych ar y car" is not particularly emphatic.
Compare "Wnes i ddim edrych ar y car" and "I did not look at the car" -- where in both cases "wnes/did" does not serve to emphasise but merely helps to form the negative sentence. In Welsh, "to do" can also help to form not just questions and negative sentences but also regular (unemphatic) positive sentences.