To complete Level 24, you must generate full spools of thread by matching three or more partial spools on the puzzle board and then use them to knit the corresponding color sections in the pattern at the top.
You can only use a spool for knitting once it is full. You must make matches of three or more partial spools on the lower grid to create a usable, full spool. The level is marked "Hard," which means you need to plan your matches carefully to ensure you can create the colors you need. There is no time or move limit shown, but you have a limited number of lives (4/5 at the start), so avoid incorrect moves if that is a failure condition.
Prioritize your matches based on the colors needed next in the knitting pattern to work efficiently. Look for opportunities to create chain reactions by making a match that causes other spools to fall into place and form new matches automatically, which clears the board faster.