How to join Tauren Chieftain's three cards?

When writing a card, click the card down button to join.

The effect of Tauren Chieftain's three cards is that when you build your deck, you can combine three cards into a deck to join the deck.

The usage of this card is that you can bring some targeted but not universal cards. For example, the duke can target mine technology, but it is almost useless to play fast break. Snake soft can be used to deal with miracle thieves, but a profession without a knife is damaged. Wandering evil spirits only eat cards, and playing other occupations is of little use.