"nikogda" and "nekogda"

[aunil.livejournal.com]

Hello everyone :)
I'm an italian university student, and I've been studying Russian for three years now.
This year they've explained us the differences between NIKOGDA and NEKOGDA, but I'm not sure I understood.
Anyone willing to help? :)

Thank you in advance :)

Marta

Союзы

[giantantattack.livejournal.com]

When translating the English conjunction "but", how does one know when to use но or а or да?

Also, in the same thought, how does one distinguish between и, а, and да, as far as "and" is concerned?
[EDIT]: I found the answer to this last part in the community's memories section.