A proportion usually compares one quantity to another. For example I could compare boys to girls as 12 boys to 15 girls. You could use the word ‘to’ as I have done you could use 12:15, you could use a fraction 12/15. You could figure out percentages of boys to girls, or girls to boys, or girls to total children, etc.
A percentage must be a quantity compared to 100.
For example 20% means 20 out of 100, 20/100.