If you have a light housing that has a replaceable bulb, just put the bulb in the socket. If it doesn't work, remove the bulb, turn it 180 degrees, and put it back in. If you need to put a new housing in, be mindful of the polarity. LED lights are polarity sensitive, so don't reverse the positive and negative wires. Check operation before making final connections.
If you are running ONLY turn signals, the two wire is the one you need. That gives you a negative (ground) and a positive (circuit) wire.
If you are putting in running lights AND turn signals (3 wire), they share a common negative (ground) wire and each circuit has its' own positive (circuit) wire.
The LED lights are more efficient. That means they draw less current and waste less electricity through heat than "normal" bulbs. The flasher in most turn signal systems uses heated contacts to open and close the circuit (thermal flasher). Because the LEDs use less heat, the thermal flasher gets more heat pushed to it and will operate faster (blink faster). This will eventually burn the thermal flasher out. The thermal flasher will work for a short time with LED lights.
The correct (digital) flasher is made for LED lights and will blink correctly. It is a simple remove and replace plug in to the correct circuit. The LED (digital) flasher will work correctly for incandescent bulbs as well, so don't worry about mix and match in the circuit. Ask for an LED flasher for your year and model truck at the parts store. When you get the flasher, turn your turn signals on and follow the plink sound to the flasher. If you remove the flasher with the turn signals operating, they will stop flashing and go out. That is the flasher to replace.