Tenir vs Avoir
So, these two verbs mean the same. When is it correct to use "tenir" and when to use "avoir".
No, they don't mean the same. "Avoir" is 'to have' and "tenir" is 'to hold'.
Yet there are plenty of expressions where their meaning can be close or where the English uses one and French the other one.
Unless you give a precise example, there is not much ground for a more accurate answer.
I think you're confusing "tenir" with the Spanish word for "to have", "tener".
"Tenir" has a lot of different meanings. I found two webs that may be useful to understand it. https://dictionary.cambridge.org/dictionary/french-english/tenir https://fr.wiktionary.org/wiki/tenir