Learn Polish: Nie rozumiem programu. - I do not understand the program.

The verb rozumieć (to understand) usually takes a direct object in the Accusative case, which would just be program. But because we used the negative word nie, the object has to change to the Genitive case. This rule is called the Genitive of negation, and it changes program to programu.

Why does the Genitive form of program end in -u instead of -a?

Program is a masculine inanimate noun. In the Genitive case, these nouns take either an -a or a -u ending. While there is no perfect rule, foreign loanwords, abstract concepts, and technology terms usually take the -u ending.

Why does rozumiem end in -m? Do not most verbs for 'I' end in -ę?

Yes, most verbs for 'I' end in -ę, but rozumieć (to understand) belongs to a small, special group. Its 'I' form ends in -em. You will see this same pattern in other very common verbs like wiedzieć (to know, which becomes wiem) and umieć (to know how, which becomes umiem).

Where is the word for 'I' (ja) in this sentence?