Probably the best way to start studying a language is to grasp its most common phrases.

We will start with greetings.

The most popular word to say hi informally is labas.

Another popular informal way of saying hello is sveikas, sveika, sveiki and sveikos. These words are dependant on gender and number.

Sveikas is said to one male person, whereas sveika is a greeting to one female. Sveiki is said to more than one male, and sveikos is used to greet more than one female. If the group is mixed (males and females), you have to use sveiki.

When addressing people you don't know, older people or a person of authority (teacher, etc), you must use one of the following phrases depending on daytime:

labas rytas or labą rytą in the morning,
laba diena or labą dieną in the afternoon,
labas vakaras or labą vakarą in the evening.