Try these tutorials with Photoshop
Edit photos to create new images and graphics.
Understand the differences between raster and vector graphics.

Raster images (BMP, JPEG, PICT, PNG, PSD, or TIFF) consist of a grid of pixels, as in a digital photograph, and lose detail when scaled.
Vector images consist of lines, shapes, and other graphic components stored in a format that uses geometric formulas. When scaled, edges remain crisp and sharp.