Every board is generated and solved exactly before you play.
Find your outlined area. It starts in the top-left corner. Only the connected, outlined tiles are yours.
Choose a new colour below the board. Your whole area changes to it and absorbs every matching tile touching it.
Repeat until the board is yours. Fill every tile in as few colour choices as you can.
On Daily and Challenge boards, your first run is official. Restarting switches you to practice.