Your braided main line is thin, visible and has no abrasion resistance, which is exactly why you tie a leader to the end of it. A leader is just a length of the right material between the braid and the lure or fly, and building a good one is a simple, high-value skill.
Material and length
For most inshore fishing, a fluorocarbon leader (for its invisibility and toughness) of a few feet, joined to the braid, covers it. Go longer and lighter for clear water and spooky fish (albies and bonito want long, light fluoro), and shorter and heavier around structure and teeth. Use mono when you want stretch and shock absorption.
Bite guards and wire
When the target has teeth, bluefish, wahoo, sharks, add a short bite guard of heavy fluorocarbon, or a wire trace for the toothiest fish. This short shock section saves your lures and fish.
The connections
A leader is only as good as its knots. Connect braid to leader with an FG knot (thin and strong) or a double uni (quick and easy); join to a heavy leader with a slim beauty or Albright; and tie the lure on with a Palomar or a loop knot for action.
Tip Match your leader to the fish and the water, not habit. Clear, calm, spooky conditions call for a longer, lighter leader; heavy structure and toothy fish call for a shorter, tougher one. Carry a couple of spools and adjust.