1. The full list of persons in the past tense looks like this. The units so far have only covered some of these, but this list may be useful.
Mi wnes i siarad - I spoke
Mi wnest ti siarad - You spoke
Mi wnaeth o siarad - He spoke
Mi wnaeth hi siarad - She spoke
Mi wnaethon ni siarad - We spoke
Mi wnaethoch chi siarad - You spoke
Mi wnaethon nhw siarad - They spoke

2. You may come across short forms of the past tense where the ending is put straight onto the verb. The endings are similar to the above apart from he and she, which end in -odd. You'll see these forms in particular when reading.

Mi siarades i = I spoke
Mi siaradest ti = You spoke
Mi siaradodd o = He spoke
Mi siaradodd hi = She spoke
Mi siaradon ni = We spoke
Mi siaradoch chi = You spoke
Mi siaradon nhw = They spoke