MTG

I've recently started playing magic on MTGA, mostly played with a life gain starter deck that I modified using couple suggestions that I found on the internet. Now that the new season has started I thought I should try making my own deck, but after hours of staring at the card list I am lost, it seems like there are both too many cards and too few if you look for specific interactions if I try to theme the deck around it. How do you pick the core cards, where do you draw the inspiration from and how long does it take for you to build a deck?