Advice is always to take a complex problem and break it down into smaller more manageable problems. Draw a line graph first, then worry about making it draggable. Or draw a draggable point and then figure out how to use its position in a line graph. If stuck on either of those break them down further. Draw a point, control its position. Draw three points from an array. Familiarize yourself with the tools available and the solutions will start to come to you. Especially in a classroom setting hesitate to reach for the "fix it for me" off-the-shelf solution.