You can scan up to 5 different Amiibo a day to receive gifts such as weapons and gold. Fire Emblem amiibos will earn you Silver weapons while other amiibos could be random resources. The right Joy-con and the Switch Pro controller have built-in sensors that can scan the amiibos you place on them as shown below.
To receive Amiibos, head back to the game’s main menu then go to Extras > Presents > Amiibo. Tap the Amiibo to receive your gift. This is automatically added to your convoy/ inventory.