a ratio is how many of one thing there are per another thing. for example:
we have 30 cupcakes. 10 are vanilla and 20 are chocolate. so, the ratio of vanilla to chocolate is 10:20, simplified to 1:2. there is 1 vanilla cupcake for every 2 chocolate ones.
every fraction is a ratio. for example, 10/5 = 2, because there are 2 fives in 10. or 64/16 = 4: there are 4 sixteens in 64.