problem about ffmpeg's parameters

[langkejian]

I am doing transcoding by using ffmpeg,but one problem was met.
Could you please help me if you coule know the answer?

Parameters about -f,-target,-vcodec and the suffix of the output file's
name,they are all relative to the code format of the output file.

What are the relation and difference among them?

ps:sorry ,my English is so poor.