Questions & Answers about Nie rozumiem tego słowa.
Because the verb already tells you the subject.
Rozumiem means I understand:
- rozum- = the verb stem
- -iem = 1st person singular present-tense ending
So Nie rozumiem tego słowa. already means I do not understand this word.
You can say Ja nie rozumiem tego słowa, but ja is usually added only for emphasis, contrast, or clarity.
Here is the breakdown:
- Nie = not
- rozumiem = I understand
- tego = a form of ten / to / ta meaning this or that, here in the genitive singular
- słowa = a form of słowo (word), here also genitive singular
So the sentence is literally something like:
Not understand-I of-this of-word
That sounds strange in English, but it is normal Polish grammar.