JourneyMap is a delightfully useful mod that records the world map as you explore it. It allows you to set waypoints, keep track of what is where, where you last died, etc. Normally the JourneyMap is opened by pressing 'J'... however, for some reason the keybind needs to be set manually first.
To do this you will need to go into Settings > Controls in Minecraft, locate the JourneyMap section, and set the opening of the map to 'J'.