Are these correct?
I didn't talk to my friend yesterday.
Watashi no o-tomodachi wa kinou shaberanakatta desu.

I have to learn Japanese.
Watashi wa nihongo wo manabu hitsuyou ga nakereba narimasen.
Or
Watashi wa nihongo wo manabu hitsuyou ga aru,

How can i say
* I left without saying goodbye* ,
* I received a letter from a friend from Oregon*

Thank you for your help...^^

Question

Are these correct?
I didn't talk to my friend yesterday.
    Watashi no o-tomodachi wa kinou shaberanakatta desu.

I have to learn Japanese.
    Watashi wa nihongo wo manabu hitsuyou ga nakereba narimasen.
    Or
    Watashi wa nihongo wo manabu hitsuyou ga aru,

How can i say 
* I left without saying goodbye* ,
* I received a letter from a friend from Oregon*

Thank you for your help...^^

Answer

I have to learn Japanese.
→"Watashi wa nihongo wo manabu hitsuyou ga aru."
Or if you want to say more polite, you can put "aru" into "arimasu".

"I left without saying goodbye."
sayonara wo iwazuni kaetta.

"I received a letter from a friend from Oregon*
Oregon no tomodachi kara tegami wo moratta.

I think:)

Answer

I didn't talk to my friend yesterday.
Watashi no o-tomodachi wa kinou shaberanakatta desu.
->Watashi wa tomodachi to kinou shaberakanaktta desu.