I hear the phrase 'flat the 5th" and people talkin about 5ths and 7ths and i was just wondering what the hell are they talking about....

I have looked at music theory but i cant understand it...

thanks in advance
those numbers are the degrees of a scale. C major scale for example:

a b5 in that scale would be a Gb. The 5th note of the C scale.
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im simpler terms the 5th and 7th are refered as dominants in relation to a tonic(starting position). Going to a 5th orr 7th means you go up(modulate) 5 keys over your tonic. I assume flating the 5th means you just bring it down a half step of that dominant position
also if you're reading leadsheet, having 7 usually means a flat 7 and of course b5 means w/ the lowered 5th, so C7b5 you'd play C E Gb Bb for the chord