A modal verb is a verb that shows intent, possibility or necessity. They are a type of auxiliary (helper) verb and they are typically used alongside the infinitive form of the main verb.
CHTÍT* - want
MOCT* - can, be able to
MUSET - must, have to
Both chtít* and moct* are irregular verbs (follow the irregular conjugation).
chtít*: já chci, ty chceš, on/ona/ono chce, my chceme, vy chcete, oni chtějí
moct*: já můžu, ty můžeš, on/ona/ono může, my můžeme, vy můžete. oni můžou
For example:
Chci jít do kina. - I want to go to cinema.
Můžu studovat češtinu každý den. - I can study Czech every day.
Musím pracovat. - I have to work.
Negation
Negation is formed by adding ne- in front of the modal verb. For example:
Nechci jít do kina. - I do not want to go to cinema.
Nemůžu studovat češtinu každý den. - I cannot study Czech every day.