What is the difference between ratios and fractions?

Both are different ways to represent an amount of something. Fractions show how much of a whole item there is for example 2/10 2 parts out of a total of 10. On the other hand, a ratio describes one amount relative to another, for example 1:3 meaning 1 part of one amount corresponds to 3 parts of another amount, a good way to think about this is when making squash, you take an amount of squash, such as 10ml and add another amount of water, for example 100ml, the ratio would be 10:100, which can be simplified as 1:10, since there is 10 times more water as squash.