We're going to talk about how to build a Magic The Gathering Deck that you can play against other planeswalkers. We'll start with the basics. What are required in a playable Magic deck?
A Magic The Gathering Deck consists of a number of Magic cards which range from 60 cards to as many as you want. We usually suggest building a deck of 60 cards, because the proportion is more even. This makes the probability of getting a key card more even.
Basic content of a Magic Deck is divided into three parts. One third of the deck is Lands, another one third should be Sorcery, Artifact, Enchantment and Instant and the last one third should be Creatures. The Lands are used to produce Mana for casting spells. There're cards other than Lands that have the ability to produce Mana. Of course you can use these Mana producing cards instead of lands, but at least a half of this one third of the deck must be free of Mana cost. Otherwise you'll never get the first Mana.
The next one third of the deck which consists of Sorcery, Artifact, Enchantment and Instant is the tools you can use. You can use these to assist your attacks or to construct combo. If you do not need too many assisting spells or combo, you can replace them with attacking spells or creatures.
The last one third which is the Creatures in essence these are the cards you can use to hurt your opponents. If you've got many helping spells, it does you no good if you can not damage your opponent. Of course you have the right to replace creatures with attacking spells, but it's not very reasonable to have no creatures at all, unless you have other method to block the attacks of opponent's creatures. If you choose strategies that can beat your opponents without damaging them, please make sure that it is feasible and have a good chance in winning.
One thing you must bear in mind when you are building decks is that except Basic Lands, there must not be more than 4 cards with the same name in the same deck.
I personally prefer using a more evenly distributed deck. As you gain experience and knowledge you will learn how to construct combos to assist your creatures' attacks. Combos can be very devastating and I think structuring them according to your unique strategies to beat your opponent in a calculated way is a lot of fun. Magic The Gathering Cards are designed in a very sophisticated mathematical way, there are complex relationships between cards. As you start your journey of building decks you'll discover these relationships and the multiplying dynamics between different spells. And this would be a crucible in building a powerful Magic Deck.