HOW TO FIND CRYSTALS:
Right now the Green, Blue And Lava are the only naturally occurring crystals. To make red, you must smelt a blue crystal. To get the DARK SABER you need to add netherite onto a hilt, then burn a red crystal, then combine them in a smithing.
To make a saber, find the ore, then put one iron on the top of the crafting grid, one to the middle right, and one at the bottom, then place a stick in the middle. Finally put a redstone dust on the right.
After doing so, combine your crystal and hilt using a smithing.