JustlyHarmonized

Hello, my name is Do. I have been teaching guitar for 1 year now. I am 16, and i just recently, in the past year encountered microtunings. I was immediately stumped.... My only problem is

the numbers on either side of the ratio..... I just cant figure it out. Is it like this?

a=440Hz, so a 1:1 ratio is: one cent to one cent, and 4:3 would be the D in the next octave?
If so, How would you set a root note?

I probably made a complete fool of myself, My father understands it my old theory teacher understands it, but i am 99% stumped....

thanks

DOH!