The only requirements for a complete sentence are a subject and a verb. Just like in an English sentence, in Spanish the subject (when stated) comes (usually) before the verb. There are many other parts of speech that can make a sentence more complex, but for now, simply think of a sentence as:
Subject + verb + rest of sentence
In the following sample sentences, the subject is underlined and the verb is in bold type.
Julieta bebe una coca cola.
Julieta drinks a Coke.
Tú compras un televisor.
You buy a TV.
Berto y Gonzalo viajan a Lima.
Berto and Gonzalo travel to Lima.
Diego trabaja en un hospital.
Diego works in a hospital.
Remember that the subject is the person or thing that is responsible for the action of the verb. The verb is usually an action word and will be conjugated in the correct form to go with the subject.