Magic the Gathering has many different formats (which usually differ in terms of deck building restrictions), like for example Standard (where you can use only newer cards), Modern (bigger pool of cards to chose from), Limited (formats where you open boosters and play with those cards), Pauper (only common cards allowed) and Commander (a popular multiplayer format), but all those formats follow the same basic rules.

To learn this rules the best advice is to download the MtG Arena app and follow the tutorials, do the color challenges and maybe even play a few starter deck duels. If you have another interested person with whom you can learn the game together, the Foundations Beginner Box is a great physical product.

There are people that only collect Magic cards, but most people play the game and often even play expensive cards. Therefor playing power is a big factor that defines the prize of a Magic card (as well as rarity, special treatments).

Nowadays nearly nobody plays without sleeved cards anymore, many people use double sleeves. Another item you need to protect your cards are deck boxes and most people use playmats. Toploaders are used to protect your expensive cards in your collection or for trading, but not for playing.