why "yo soy" but not "yo tengo"
when do i need to use yo and when not?
2 Answers
Yo soy and yo tengo the yo is not required in any of them nor any other first person verb congugation as the verb congugation makes it redundant, you only use the personal pronoun in some cases to avoid ambiguity.
There are already countless threads which deal with this topic.
Have a look at this one, for example: on the subject of subject pronouns
If you want further discussions, you could also try doing a search of prior threads with the key words subject pronouns.