This is the 6558th most frequent Polish word.
d
In Polish, "d" is the fourth letter of the alphabet and has no standalone meaning as a word.
The word 'do' in this sentence is used as a preposition indicating direction towards a place.
Idę do sklepu, żeby kupić owoce.
I am going to the store to buy fruits.
The word 'd' here refers to a shortened form of 'danny' which means 'given' or 'specific' in Polish, used in formal contexts.
Zrobiłem zadanie domowe i danny test.
I completed the homework and the given test.
'Do' serves as a preposition indicating the object of the action 'called'.