Questions & Answers about Napište své příjmení.
Napište is the imperative form of the verb napsat, meaning to write down / to write completely.
More specifically, it is the 2nd person plural imperative:
- napiš = write! (to one person informally)
- napište = write! (to several people, or to one person formally/politely)
So in this sentence, it functions as a command or instruction: Write ...
This is about aspect, which is very important in Czech.
- napsat is perfective: it focuses on the completed result
- psát is imperfective: it focuses on the process or ongoing action
So:
- Napište své příjmení. = Write down your surname / fill in your surname
- Pište... would sound more like be writing, write repeatedly, or it may fit a different context
On forms, signs, and instructions, Czech very often uses the perfective imperative, because the point is to complete the action.