Tengo todo lo que necesito

Tengo todo lo que necesito
 

Hi, I'm having a little problem wrapping my head around sentence such as this "tengo todo lo que necesito" it translated as "I have everything I need" but what's that extra "lo que" for? Does the translation left out the "what" for "lo que"?

Or this sentence "No tienes por qué hacerlo" supposedly means "you don't have to do it" but with that extra "por qué" that make my head hurt😅🙏

todo lo que = everything that / all that (which)
That last word 'que' is used very often in Spanish. It can mean 'that', when used as a conjunction, or 'which', when used as a pronoun. It's kind of difficult to explain to an English speaker, because we would omit the conjunction (not say the word 'that') in this case.
When preceded by 'lo', the meaning becomes 'that which'. Once again, in English the phrasing can be omitted to convey the same meaning.

The Spanish word that means 'what' is spelled qué. Note the accent mark, which is there to differentiate it from the conjunction/pronoun 'que'.


EDIT (to answer the second question):
In the next sentence you posted, you're dealing with the words 'por qué', which mean 'why', when used as an interrogative. When not used to form a question, the two words can be translated as 'reason'.
I would revise the English translation to "You have no reason to do it."
(English and Spanish rarely translate word for word.)

If you were to write "No tienes que hacerlo," it would mean "You don't have to do it." An obligation is being withdrawn here.

Thank you so much