Install the TagMo.apk file on your Android device. This makes it so that you can install apps that aren't on the Google Play store. On your Android device go to Settings > Security > Unknown Sources (turn on). Okay, so you got your stickers and phone with NFC writing, now what? I'll let you guys google that one, they aren't hard to find. bin files of the amiibo you want to put on your sticker. You can also buy blank ntag215 stickers from me on my website if you live in the USA. Mine came with 11 ntag215 stickers and got to my house in about 2 days Only NTAG215 works, 213,216 and other common stickers DO NOT WORK. I bought mine on Amazon because I didn't want to wait for 1 month to get them in from China. NFC Ntag215 stickers - these are little stickers that have a specific type of nfc chip in them that you can buy for really cheap.

EDIT: May 2020 - You can now use Apple iOS phones with the app CattleGrid or the app Placiibo! NFC writing capability - generally this means only Android phones with NFC, but apparently it is possible to buy an NFC reader/writer for PC but it is more complicated. There are 3 requirements for making amiibos you can use on your Switch/Wii U/3DS.

Nfc amiibo animal crossing download