Gelatin has a shape when it's cool. The proteins hook onto each other and build a structure. The yellow is a drop of sweetened lemon-flavored liquid. When the gelatin cools again, the proteins go back into their shape. But now they have trapped a drop of the liquid.
Proteins are strong - like building blocks.
They get their strength from getting tangled up tightly in each other. Gelatin is a liquid that is trapped and suspended by a solid. That's the reason it jiggles. It flows like a liquid but is pulled back into shape by the solid protein. There are lots of other colloids in your house.