Et tū, Brute? Venī!

When we address someone directly, in Latin we use the VOCATIVE code for the name. Names and adjectives ending -us will change to -e: Brutus changes to Brute. Names ending in -ius will change to -ī: Cornēlius changes to Cornēlī. All other vocatives look the same as the nominative. Easy, right?
So far our verbs have been INDICATIVE, from the Latin word indicat, 'indicate, point out'. The indicative is used for statements of fact. Our verbs have all ended in -t, for the 3rd person singular: he/she/it ______s.
Now we also have the IMPERATIVE, from imperat, 'command'. When you tell someone to do something, in Latin, there is no -t. Take a look.