The structure of Spanish verbs is essentially similar to that of English, but there are so many more verb forms than English verbs because they are conjugated according to person and number as well as tense.
The form of the verb often gives the person and number of the subject, so if the subject is a personal pronoun, the subject is often omitted.
I live in the UK.
We live in the UK.
In the two example sentences above, the subject is omitted and the sentence begins with a verb.
Since Vivo is the first person singular form of the present tense of the verb vivir, we know that the subject of the first example sentence is the first person singular. Also, since Vivimos is the first person plural form of the present tense of vivir, we know that the subject of the second example sentence is the first person plural.