mynd is one of the five major irregular verb-nouns in Welsh (bod, mynd, dod, gwneud, cael) where their conjugated verb forms can look very different from the original verb-nouns. Some of their verb endings also differ from those used with other verbs.
If you write out some tables from the course notes of how they conjugate, you will see that dod, gwneud, cael, mynd have a lot of similarities, although some differences, too. bod is really out on its own.
(Edited to group dod, mynd, cael, gwneud together.)
Is mynd that different? I always assumed you could get to dod/gwneud/cael by adding d/gwn/c to the front of the conjugated form of mynd (ewch/dewch, es/ces, for example come to mind). Might have to check I'm actually using the right words for things if that's not generally the case.
Mynd is an irregular verb in Welsh, and it's form changes depending on the tense and the subject. In this case, it's past tense. It's like in English, we say "I went to the shops", not "I go to the shops", if we're talking in the past (we also conjugate different based on the subject too - "I walk" but "He walks").
As already mentioned, in the UK the word used is 'pub'. However since 'tavern' is used in some other countries, along with 'inn'. This course accepts all three as a translation of 'tafarn'. If you come across one that doesn't please report it and we'll fix the sentence.