If you have any Legend of Zelda-related amiibo, you can place them on your 3DS’s bottom screen while at the Title screen of the game. Once per day, per amiibo, you can get a reward for using you amiibos. These rewards are almost always weapons for the Warrior related to the amiibo you used, but you can also get Rupees from using them, as well.
Make a point to use your amiibo every day. Which weapons drop and how strong they are is completely random, so you never know if you’re going to land a super-powerful weapon for them. You receive weapons of the highest tier you currently have unlocked. For example, if you have Link’s White Sword, you are guaranteed to get one of Link’s White Swords and not his Knight’s Sword.
Even if you end up with weaker weapons, you can sell them off and add to your Rupee pool. With Rupees being so vital to strengthening your Warriors, you’ll almost always be desperate to get your hands on them, and selling those weaker weapons helps with that.