Literally buy it download the software and plug it in. It will start an update and stop halfway, it says don't unplug it/ remove but do exactly that once it stops (if it stops may not happen to all of them) then plug it back in and the update should finish.
Put the power puck on there and choose the backup option. This will create a new folder in C:userdocuments (iirc) called powersaves for amiibos, and that's where you put your obtained amiibo bin files (best site is NFC ____ the blank is the place you put your money, think about it, then google the name with the amiibos you want such as Zelda etc). You don't have to rename them or anything and I haven't for fear of it not working but it's just a file name so no biggie. Make sure it's just the .Bin file and not in a zip.
Once placed in the folder the program created you select the load option to load your selected amiibo and scan it like you would any other amiibo. It will occasionally say failed or seem like it didn't write it so sometimes I'll write the same file twice to be sure but I've never had an issue with it not being read by the switch.
I suggest saving before scanning each unique amiibo In case you don't get the drop you want you can just reload to right before you scanned it and scan again. Then save once you get a drop you want and load a different amiibo onto the puck. Wash rinse repeat.
Sounds complicated but it's dead simple. It's how I have gotten near everything in the game including the fierce deity set and sword and currently working on the last piece of skyward sword gear and the goddess sword.
Edit: just wanted to clarify that this works for the switch as that's what I have never had a Wii u.
If anyone needs help or directions/more instructions just shoot me a pm and I'll do what I can.
Tl:Dr download program, update unit, get amiibo files, place puck on it and back up the blank puck, find folder it created for backup, place obtained amiibo files in folder, load onto puck, Scan puck switch file and repeat.