Re: Prewired 16x2 blue display
...or more specifically,
or an upgrade if you like,
As to soldering pins to the board, I might suggest first tinning the pins alone; if you have some soldering flux, a trace amount on the circuit board holes won't hurt though optional. Then, with the board held by a vise or similar, use pliers to hold the pin and place it about 3 or 4mm (1/16"?) into the hole. With a small drop of solder on your iron's tip, heat only the tip of the pin until the solder wicks onto it. Then, immediately draw the pin and the iron outward together to a suitable mounting position for the pin. You can and should roll the hot iron tip around to touch the circuit board, at which time the solder will wick over to the circuit trace. REMOVE HEAT as soon as the wick happens. Blow on it, cool it, etc and you will be OK from there to continue to the next one.
Hint: Not all pins are used or necessary.