Ecto : normally lean, has difficulty gaining mass...toughest type to be a huge bodybuilder with.
Mesomorph : good size, puts on mass fairly easily, usually genetically advantaged over other types.
Endomorph : larger structure, usually more inclined towards gaining bodyfat.
Most people are a combination of two of them...ecto-meso, meso-endo, etc. You may look like an ecto now, but actually be a meso...which you will find out after training for a while. We all had to start somewhere...noone on this board got looking that way overnight, and neither did anyone in your gym. It takes years of training and dieting. So get started.