But the utility of a copper subscription is limited. Basically, it only works in limiting the card selection when you get matched with someone with a copper or no subscription. Even players who get the silver subscription have the problem of getting matched against a gold subscription and getting lots of unfamiliar cards.
Really, if you want to learn new cards without the pressure of a game against a live opponent, the quickest way is to play bots. Creating a table and using the familiar cards setting is difficult as automatch for full random ranked games accounts for the great majority of the community here.
Long-term the campaign will address this, although a decent AI is needed there. For now, the best way I can think to learn new cards is to play bots. It's not great, but at least you can see what the cards do without any time pressure as you read them and figure them out.