What do the modal verbs ' must ' and ' mustn't ' express in a sentence?

katarina.bojnanska

cupk8ty

janetgalindo

carolina.souto.giacomin

anymilagrero

frosina.aleksovska

harikleia95

ngmindymmu

jshea

natal.berezovskaya

joshi2

sarada3na93

ruka.vang

dmrp201083

Farkavcova

anna.katsubina

rawda.zaky

fianojosa

aakkam92