ive found that when you are new to magic, start with "kitchen table magic". This is just very casual friendly play which is largely non competitive and between friends and such. go to your friday night magic stuff at the nearest games store.
For decks, for complete newbies you'll want to start with the pre-made decks and start battling them against each other. Doesnt matter if its just you either, just play against yourself. Make sure to read the little pamphlet that comes with them because it tells you how to play the deck.
Buy 1-2 booster boxes eventually, just save up for it and buy it. This gives you a pretty good base of cards.
Now while you play, take a good note of what cards work really well and what thoughts are crossing your mind. You'll notice that during the first X turns you might just be sitting there playing mana. How can you get around this?
You'll notice that certain cards are just too costly and you never manage to play them. You'll notice that some of them are supposed to be game winers but hardly do anything.
You might notice that some cards work exceedingly well together. Now you start fixing these beginner decks. Start replacing cards.
Read up on deck building strategies such as: Mana Curve and Rule of 9.
Make sure you are reading other peoples' decks. Comment on their decks, tell them you are very new, and ask them to fully explain their thought process behind the deck. Chances are, every single card is in there for a very specific reason.
Back in the old days (im 24, this is back when I was 13-15) I used to play against my friends. I started with a single 7th edition deck. I bought a few deckboxes like Beatdown and Deckmasters. I bought a couple odyssey fat packs or something. I bought a few boosters. I traded amongst friends. But the way we played was to load down a deck with as many big game winners as possible and call it a day. Sometimes they were too big so we'd take them out. Sometimes the strategy would never work out too well so we'd have to add in various cards that could all work well together no matter which hand/order you drew them in. Those were simple days.
Now, you go with 1-3 MAIN strategies. You use the rule of 9 to pick 9 cards (IDEAL CONDITIONS). you get 4 copies of each of these 9 cards. the rest is mana. Then you replace as much basic lands as you can with "good lands". If its doing more than JUST generating mana, its better than a basic land.
You'll see when you read about it.
Just make sure you keep reading and looking up different cards and effects. You cant just willy nilly assume that some card exists, because its difficult to do things that way. Its better to know your own arsenal backwards and forwards and be able to use it wisely.
For example: Gray Merchant of Asphodel in a mono black devotion deck.
