Saber saws, also known as jigsaws or bayonet saws, are widely used for making both straight and curved cuts, sometimes very intricate and complex ones. In addition to cutting wood and metal, saber saws can also cut through brick, plastic, leather and ceramic tile, depending on the kind of blade used. In general, the more teeth a blade has and the finer those teeth are, the smoother the resulting cut surface will usually be. Other variables of saber saws are how much power -- measured in amps -- they are capable of and how fast they can operate. This speed refers to how many strokes per minute the blade moves.
Many saber saws come with the option of a scrolling mechanism, which lets you turn the blade around 360 degrees while cutting to produce very detailed shapes. If you want to start a cut in the center of your work and not from the edge (for example, you want to cut a square shape in the middle of a piece of wood), mark the shape you want to cut, and tilt the saber saw forward so that the nose of the saw is touching the surface. Holding the saw with both hands, turn the saw on, and carefully lower the rear of the saw, allowing the blade to cut through the wood, then continue cutting along your lines. Another use for saber saws is to bevel the edge of your work, which can be done by cutting at an angle of 10 or 20 degrees.
If you don't trust yourself to saw straight lines -- especially where a straight line is very important to the appearance of the finished product -- you should use a straightedge guide. Alternatively, you can take a straight piece of wood, clamp it to your work and use that as your guide as you move the saber saw down the length of your work.