Chuala mé . . . I heard my dad coming back from the shop in the car.

mo dheaid - - my dad. (No need for a capital d here. If you were using deaid as a proper noun "A Dheaid! Cá bhfuil tú?" you would use the capital D.) I know the dictionary gives daid and so mo dhaid would seem the correct spelling. Nevertheless I have never heard the word pronounced other than as I spell it. I hear mo dheaide also. I look forward to your comments. What do you think?

ag teacht - - coming is a form of the verb called an t-ainm briathartha - - the verbal noun. This will form the subject of another lesson later.

ón siopa - - from the shop. (ó + an + siopa)
sa charr - - in the car (i + an + carr) (more . .)
Both of the above constructions involve the réamhfhocail simplí - - simple prepositions and they will be treated in more detail in another lesson. NIG discusses these in Chapter 29, page 134.