"You read my books."
Translation:Tu leggi i miei libri.
Why does [You read...] corrects me to [Lei legge...] instead?? I said [tu leggi i miei libri] and says it's wrong... Isn't it that 'Lei' means 'She'? Otherways said... [You] follows the 2nd conjugation (tu), while 'Lei' (He/She) belongs to the 3rd one... or am I wrong? What am I missing?
Generally, you can't. Without context you just can't be sure which. So either is acceptable.
Translating from Italian to English gives you context from the verb. If the verb is in 2° person plural, it is "you (all)" .
English to Italian translating "you eat" it could be either. But translating "you are animals" it would be voi because of the plural "animals"
In conversation, you usually will know because of the context