The concept of support and resistance is simple. Support can be thought of as a floor for the price while resistance can be thought of as the ceiling for the price. When the price breaks through a resistance, that level becomes the new support level. The reverse is true when the price breaks through a support level.
The best use of support and resistance is during trend trading. If the trend is up, you want to go long at support and take profit at resistance. If the trend is down, you want to go short at resistance and take profit at support.
Support and resistance levels are sometimes not exact price levels. Many times, they will be a small range of prices. Once the price clearly breaks past that range of prices, support or resistance is to be considered broken.
Support and resistance should be used as reference points when looking at a forex chart and trying to make a decision. They can give you a good idea of where to put your stop loss or take profit orders.