New Player Guide to Build a Deck
First you need to decide which format you wanna play in, as beginner standard makes the most sense.
A good cheap deck you can build from the get go is probably mono blue tempo right now. Sure you can try coming up with your own deck ideas, but you will waste precious wildcards and in the end get stomped by meta decks anyway.
If you wanna build some decks tho, most important is to figure out your wincon and center the whole deck around it. Dont do the classic mistake of “add some card draw here, some removal here, and especially avoid nonbos / cards that void each others purpose, like one card that empties the graveyard while the other cards can come out of the graveyard” plus always be careful with how much removal you put in. Its important, yes, but sooner or later you will run into decks that dont play any creatures and you will have a very bad time. Same goes for discard spells. Its tempting to have 4x duress, but thats a beginners mistake, as most of the time the opponent will topdeck what he needs eventually, while you wasted a card slot that could have had much more impact.
If its an aggro deck, every card should focus on getting the opponent dead asap. No interaction or value, empty the hand, shoot face and win, minimal interaction. If you play control, make sure you stay alive and stabilize the board. Combo decks are about protecting your combo pieces and actually finding them, while staying alive as long as you need to combo off.
Find a good land count (25 is a good average) and lower it for aggro and increase for ramp/control. Most importantly, make sure you have a good curve. You should be able to play a spell every single turn. 1Cmc spell on turn 1, 2cms on turn 2, thats the most ideal way to play magic. You dont wanna sit there doing nothing for 4 turns because you only put expensive cards in your deck. So depending on the deck, the higher the cost of the card, the lower the amount of said cards. You only wann have very few very expensive cards.
But like I said, the economy in this game really punishes you for experimenting. Unless you wanna spend real cash.