The first class you get is Mage which pretty much introduces you to the basics.
The way the classes work is that they all have thirty health and a special hero power which may allow them to heal, deal damage, gain extra health, and draw a extra card.
The goal of hearthstone is to defeat your opponent which you have to get their health down to zero or make them use their entire deck. The way you do this is by playing the cards in your deck to deal damage and defeat them.
If your cards are lacking that punch, and you don't have no good spells it's time for you to craft, the way crafting works is that you get dust from decorating other cards or doing other miscellaneous things , you can even craft legendary cards at a higher cost of dust.
Legendaries are incredibly great cards with special affects, they are extremely hard to get but are worth every moment. Some legendaries can even can even change your cards. Legendaries have high damage or have a even greater ability.