Hand planes are used for smoothing out the surface of timber, making it flat and/or reducing the thickness. There are also specialist planes available for rebating, working in tight corners, scraping and loads of others! Before routers planes with interchangeable shaped profiles were used commonly to apply moldings and decorative edges to timber. I always keep my plane irons razor sharp with a bench grinder and Trend fast track sharpener. (Click here for more info about the sharpener).
There are several different types of plane you will come across during your career as a carpenter (rebate, bench, jack, jointing). The most common used on site and during finish carpentry are the Block plane and Stanley no.4. These are enough for general carpentry. The 'Rolls Royce' of planes are made by a company called Lie Nielson, but these are more suited for fine joinery and cabinet making work.
Using a hand plane
Always make sure before you start planing anything that the blade is square to the base and only very slightly protruding. Never assume it's OK because if it's set too deep you'll dig the blade straight into the timber and have to spend a while planing that out! To check, turn it upside down and hld it by the front handle with the rest of the tool away from you. From this position it's easy to see exactly how much of the plane iron is out and whether or not it's square. You can easily adjust the depth and squareness with the lever and dial on top of the tool.
When planing boards that have been joined together it is sometimes suitable to first plane across the grain to flatten the surface before then going in the same direction as the grain to smooth it out. In addition to going in the same direction as the grain for a glass like smooth finish, when using a plane always go 'with the grain' and not against it. This is the same principal as when shaving your face, you go in the same direction as the hair grows. Planing against the grain although going in the right direction can result in 'tearing' instead of cleanly cutting the timber. Check which direction the grain goes by looking at the side of the timber you are about to plane. Some timbers are more likely to tear than others like Idigbo for example and in some instances, often around knots the grain will change and you may find it best to work towards or away from the knot in all directions in order to prevent tearing the workpiece.
The rebate plane has a 90° shape, a blade that goes all the way to the outside edge and a fence to set the width/depth of the rebate with.
I don't own a rebate plane, I've never really needed one on site, they are more commonly used by bench joiners and cabinetmakers.