to understand
The French verb 'comprendre' is used in much the same way as the English verb 'to understand'. Examples include, 'Je ne comprends pas' which translates to 'I do not understand' and 'Tu dois comprendre' which translates to 'You must understand'. It's often used in conjunction with nouns or pronouns.
I can't understand this book.
This sentence expresses inability to understand the content of a book, it follows the structure Subject + ne + verb + pas + object.
Can you understand what I'm saying?
This sentence is a question aiming to check if the listener is able to understand what the speaker is saying. It follows the structure subject + verb + object + verb + subject.
They don't seem to understand the situation.
This sentence expresses that a group of people (they) appear not to understand a certain situation. It follows the structure subject + ne + verb + pas + verb + object.