"Young people have to go to school."
Translation:Junuloj devas iri al lernejo.
It seems to me that your native language is Português, right?
According to the dictionary of lernu.net,
- "devi (must)" = "dever" in Português
- "bezoni (need)" = "necessitar" in Português
I don't speak Português. So, I cannot confirm that they have the exact meaning in Esperanto; They may not!
I think it's better to lookup these two words in an English-Português dictionary.
Kore dankon, noureddin95! How do you know that i'm lusophone? Haha... So, in Portuguese, "dever" e "precisar" can be synonymous, but "dever" can mean something about obligation and "precisar" about needing... I think i got it...
Vi bezonas tion kio mankas al vi. Vi devas tion pri kio vi havas la devon.
How do I know that you're Lusophone?! How can't I know and you have written on your Doulingo-profile that you're "brazilano". :P
I cannot understand your second sentence: "Vi devas tion ...".
In Esperanto, "devi" is always followed by an infinitive (i-verbo, a verb with the ending -i). But it's not necessary for "bezoni".
So, we say: "Mi devas fari la hejmtaskon" = "I must do the homework", and "Mi bezonas manĝi" = "I need to eat", and "Mi bezonas tion" = "I need that", but never "Mi devas tion".
You may use the great dictionary "Plena Ilustrita Vortaro" (PIV).
Good Luck! :)