An Almost All-purpose Saltwater Rig

There are as many different rigs to attach to your line as there are fish in the sea. Here's the one I use the most, and it's very common in fresh and saltwater.
There are three parts: the weight, the swivel, and the hook. The hook is at the end of what's called a "leader." It's stronger line than you have on your reel. Here, the line from the reel is 20-pound line, and the blue leader is 25-pound line.
The round weight just slides up and down the line and it's known as a barrel sinker, or an egg sinker. With this set-up, the brass swivel prevents the weight from sliding down to the hook, and when the fish bites, it can't feel the weight, as it would if it was the type of sinker that's tied on to the line.
Especially in saltwater, you may want to substitute a steel leader for the blue fishing line leader, because so many saltwater fish have sharp teeth that cut even heavy line.
You'll see many, many kinds of rigs, some with two hooks. Use whatever you like, or — whatever you see that's working where you are.