Sinkers, almost always made of lead, are designed to get your lure or bait in front of the fish. Often, this process involves getting your offering to the bottom of the lake or stream and keeping it there. When using sinkers, sometimes just a split shot or two does the trick. At other times (for example, when fishing in a moving current), you need much more lead.
A word of advice: Quit fishing when your sinker weighs as much as your fish. With so little contrast, you probably won't be able to detect a bite; and when you do, the resulting fight to land the fish is about as much fun as reeling in the Manhattan phone book.
Fish are not very particular about which sinker you use. All they care about is the food they think that you are offering them. Your choice of sinker really depends on relatively few factors:
Is there any current? (The less current, the less weight you need.)
What type of bottom are you fishing? (Is the bottom covered with rock, sand, weeds, or timber?)
What do you want your bait or lure to do? (If the bait or lure has to cover a large amount of water, you need one kind of rig. If not, you use another.)
In sinkers, shape is important. A number of sinker choices are available.
Following are the most common types of sinker:
Pyramid sinkers get to the bottom fast and dig into sand or mud.
Egg sinkers and diamond sinkers move over rocks and rubble a little easier than other shapes.
Bank sinkers and dipseys work well as fishfinders.
Split shot and twist-on sinkers are quick to get on and off and work well when you need a little extra weight.