hmmm well, nothing to it.
1 to 12, or 1:12, simply means, there is 1 unit to every 12 units of something else, an example of that say, hmmm your dad gives your sister 12 apples for every 1 apple to you, so, if she gets 24 apples, you get 2 apples, if she gets 36 apples, you get 3 and so on, 1:12 or 1 to 12 ratio for you : sister.
12:1 is the same thing as above, just switched backwards, you get 12 apples, she gets 1, you get 48 apples, she gets 4 and so on.
2 to 5 or 2:5, say you're on a bike, for every 2 miles you bike your sister bikes 5 miles, so if you bike 20 miles, she bikes 50 miles, and so on.