Machine translations are usually quite poor.
Try the translator here in our forums instead of the one you're using, though, because it'll do a better job.
There is a translator link just under the page heading, to the right of the page.
As you learned above,
yo means I. This is called a subject pronoun. More exactly, it's the
first person subject pronoun. The first person subject pronoun is always I in English, and
yo in Spanish.
The first person subject pronoun may be omitted in Spanish, because the conjugated verb fully conveys the person. Other subject pronouns may also be omitted, for the same reason.
Only the
third person subject pronouns need to accompany the conjugated verb (at least once), because the conjugated verb is the
same for each of these persons.
Have a look at the table below. It may clarify that last paragraph.
The table shows the conjugation of four different verbs in the present indicative tense. I included the verb
ser (to be) because you were questioning that verb in particular. The verb
ser is classified as an irregular verb (its conjugation doesn't follow the establish rules). The other three verbs adhere to the rules for their type. All verbs are classified by the last two letters in their infinitive (-ar, -er, and -ir).
The person is indicated for each set of verbs. As you can see, most of the subject pronouns are embedded in parentheses. Only the ambiguous third person conjugation must be accompanied by its subject pronoun (until it's understood to which person you're referring).
Thanks, María José, but you know it wasn't my intention to upstage. I wanted to give Ross a little to chew on; something to whet his appetite. 
