Learn Finnish: Minä en ymmärrä, mutta minä kysyn. - I don't understand, but I will ask.

When you make a verb negative in Finnish, you use the negative verb (en, et, ei, etc.) plus the weak stem of the main verb. For ymmärtää (to understand), the strong rt changes to a weak rr to form the stem ymmärrä. So, minä en ymmärrä means 'I do not understand'.

The English translation says 'I will ask', but doesn't kysyn just mean 'I ask'?

Yes, it does! Finnish does not have a separate future tense. You use the exact same present tense form (kysyn) for things happening right now and for things that will happen in the future. The context usually makes it clear which one is meant.

Since this lesson is about the -lle (to someone) ending, would I use it here to say who I am asking?

Actually, no! This is a very common trap for English speakers learning the -lle case. While you might think of asking a question 'to' someone, the Finnish verb kysyä (to ask) requires the ablative ending -lta or -ltä (from someone). For example, you have to say kysyn opettajalta (literally: I ask from the teacher), not kysyn opettajalle.

Do I have to repeat the word minä (I) in both parts of the sentence?