Plain mechanics rely on drag actions to move pieces. I see controls that use a mouse or finger to select and move. The objective is to place pieces together to form a picture.
You move pieces with your mouse or finger, and try to make them fit together.
Clicking and dragging is how you move pieces. The game has a zoom feature to see small parts better.
Start with the edge pieces first to save time. Most tips suggest grouping similar colors before placing them.
Q1 Controls A: Click and drag with a mouse or finger
Q2 Objective A: Move pieces to form a picture
Q3 Stated feature A: Zoom feature exists
Q4 Main mechanic A: Drag and drop pieces