Playing guitar does not have any effect on the shape or size of your fingers. If you play for any length of time though you will begin to develop calluses on the tips of your fingers. This simply means the skin on the ends of your fingers gets tougher although this has practically no effect on the appearance or use of your hands. You may notice grooves on your fingertips immediately after playing though this is normal and they will go away in a few minutes after you stop playing.