Saw blades come in many sizes and shapes, and each blade is designed for a particular purpose. Some are better suited for framing and others for trim. Some are expensive, others are inexpensive, and you really do get what you pay for. Those who purchase a cheap saw blade usually regret it and go back to the store for a higher quality saw blade. The best cutting and most durable blades have carbide tips. Each saw requires a specific size blade specified in its manual.
For cutting across the grain use a carbide tipped, cross cut saw blade with 60 to 80 teeth. Blades with more teeth produce finer cuts. Blades with fewer teeth may fray the back side of the cut.
For cutting with the grain, rip blades are used. Rip blades cut more aggressively, and a lot of power is necessary to rip thick stock. If a cross cut blade is used in place of a rip blade, the saw will work harder to get through the material. A lot of ripping under those conditions can damage the motor.
Multi-purpose blades are used for either ripping or cross cutting boards, but they will not produce a real fine cut for installing trim. These blades are good to use in your saw for most cuts, but you will want at least an 80-tooth saw blade for your finer cuts.
Thin kerf blades are used when you want a finer cut while ripping. These blades leave the edges ready to stain or require minimal sanding. Some thin kerf blades have a coating which reduces friction.