With the USB facing away from you, start at the pad to the right of the USB port. That is the first led to get power and they all run in parallel. So solder on the attiny chip first (the printing on the pcb will show the orientation) then start with that first led. Once on, plug in the board, go into bootmapper to the far right tab at the top, and then click Connect and toggle on your leds. Make sure your total led count is set to 18. Just make them all white for now and then click disconnect, the attiny will retain the settings. If soldered correctly it should light up. Unplug the board, solder your next led to the right, plug in the board and test. Keep going clockwise around the board till all leds are installed and working.
I recommend taking a tiny bit of solder and tin one of the 4 led pads. Then, get your tweezers, hold the led in place, heat up the tinned pad so it grabs the led and it should hold the led in place. Now solder the other 3 pads and then add a touch more to the first pad. It's pretty easy once you get a feel for it.
each led should take about a minute to get in place and test.