Learn Polish: Niestety nie rozumiem tego pojęcia. - Unfortunately, I do not understand this concept.

The verb rozumieć (to understand) normally takes a direct object in the Accusative case (to pojęcie). However, because the verb is negated here (nie rozumiem), the object must change to the Genitive case (tego pojęcia). This is a strict rule in Polish known as the Genitive of negation.

What is the base form and gender of pojęcia?

The base (Nominative) form is pojęcie (concept/notion). It is a neuter noun, which is why it pairs with the neuter demonstrative pronoun to (which becomes tego in the Genitive). Neuter nouns ending in -e typically take an -a ending in the Genitive singular.

Does rozumieć follow a standard conjugation pattern?

It belongs to a small but very important group of verbs that take the -em ending for "I" and -esz for "you" in the present tense. So, it is (ja) rozumiem and (ty) rozumiesz. Other common verbs that follow this specific pattern include wiedzieć (to know a fact) and umieć (to know how to do something).

Could I put niestety at the end of the sentence instead?