How to unlock Amiibo rune in Leagend of Zelda Breath of the Wild:

Before you can get the Amiibo Rune, complete the first Rune Trial / Shrine in the Great Plateau.
Go to the Main Menu screen and select “amiibo” from the options.
Accept and agree to add amiibo functionality to Breath of the Wild
You can remove the amiibo rune at any time from the same “amiibo” option on the Main Menu.
Continue your game and hold [Up] on the Left Joy-Con to select the amiibo run — it’s on the far right, with an “a” icon.
Tap the [L] shoulder button to activate the rune. You can now scan your amiibo.
A circle will appear. Tap [Up] or [Down] on the Left Joy-Con to set the distance — either far or close. Make sure you select an area that’s clear before summoning!
Place the amiibo over the [Right-Thumbstick] on the Right Joy-Con to scan.
If scanned successfully, treasure will appear!

Other Tips:

You only can use one same amiibo per day
If you want to summon wolf link but can't summon him, the reason is there are some areas where you can't summon wolf link like the inside of shrines and the Divine Beasts, towns, the open sea, and Eventide Island. try to move Link to an empty and uninhabited place and try the card again.