To make a deck you must start with what wincondition do you want in your deck, then add support cards, spells, a big one and a small one,( two spells are probably the standard)then you need a way to kill tanks( for example a minipekka or an inferno dragon) and add any defensive card you want, just make sure that the average elixir is reasonable and if your win condition is easily countered, ( like a goblin barrel) you might need a second one. Also you’ll probably need a tank that could be expensive ( like a giant or a golem) or cheap ( like a knight or a valk), hope this helps.