Charts tell you the depth of the water at low tide. They pinpoint sunken shipwrecks and other hidden hazard. They warn you about shallow water with rocks or mud banks where you could run aground. They show lighthouses, bridges, and prominent landmarks, such as buildings and water tanks. Local charts often indicate buoys, which are markers that let you approach a new channel with confidence.
Buoys are red and green.
The red buoys must be on your starboard side, the green ones to port. In coastal waters, a chart and compass can still hold their own against the fanciest computer and satellite navigation equipment found on large yachts. And they're even more reliable when the batteries go dead.