A Megaminx is a 3D puzzle with 12 sides or faces. Each side is in the shape of a Pentagon (5 sides and corners). In geometry this shape is called a Dodecahedron, but in the magic puzzle industry this is called a Megaminx.
Like most magic puzzles it is solved by matching the colors on each side with the center. If you already know how to solve a 3x3 then you certainly can make a start on a megaminx, it just takes longer as there are more pieces to put in place. For example on a 3x3 you start with a cross and the Megaminx you start with a star.