How do federal offices select its candidates?

Question

I think, by primary and general elections.But i'm a bit confused with public offices.

Answer 1

Candidates are chosen through party primaries and later through election.

Answer 2

You only get to ELECT 4 (5 if you count VP)  officials.  Prez, 1 Congressman, and 2 Senators.

These 4 go through the Party Primary election followed by the General Election in November of even numbered years.

Congressman are elected for 2 years, Senators for 6 and the President for 4.

Each state has a different number of Representatives based upon population but each state has exactly 2 Senators.

Incidentally Cabinet officials and high ranking government managers serve at the pleasure of the President - some must be confirmed by the Senate first though.