The rules for distinguishing which diacritics to choose are quite simple!
When we write ů – u with a circle:
- in the middle of words (můj, důvod, stůl…)
- at the end of the words (domů, roků, filmů…)
When we write ú – u with a comma:
- at the beginning of the words (úterý, účast, útok…)
- after the prefix (zúčastnit se, zaútočit…)
- foreign words (medúza, fúze, skútr…)
- interjection (juchú, jú…)