dominant chords

i was studying dominant chords and just tryingt to learn and understand. i just want to make sure i have this right. to make a chord dominant 7th you need to add a minor 7th, which is always 2 tones below the root. do i have that right. i.e in a C chord the minor 7th is A#, as A# is 2 tones below the root of C. i have been applying this to all chords, do i have this correct?!

i was studying dominant chords and just tryingt to learn and understand. i just want to make sure i have this right. to make a chord dominant 7th you need to add a minor 7th, which is always 2 tones below the root. do i have that right. i.e in a C chord the minor 7th is A#, as A# is 2 tones below the root of C. i have been applying this to all chords, do i have this correct?!

also been looking at dominant 9th, and i found that if you add a major 9 to a dominant 7th chord, then you have a dom9th. thus if a major 9th is 2 tones above the root, then am i correct here too?! so, in a C chord the major 9th is D. so add a D to a Cdom7 to make Cdom9. am i correct in my interpratation?