The debitive mood (vajadzības izteiksme) expresses necessity — English ‘must / have to’.
It is formed with the prefix jā- added to the third-person present form. The person who must act is in the dative case.
Man jālasa grāmata.
I have to read a book.
Tev jāstrādā.
You have to work.
Viņam jāiet mājās.
He has to go home.