My advice is to pick a color you like and stick with it, then try out the free duel color decks that have the color you like.

So if you like Red, try out the Red/Green or Red/Blue or Red/Black or Red/White decks. Give them all a bit of time and see which color identity sticks with you best.

This will mean you have 1 primary color you like (for me it was blue), a secondary color you like (for me it was black), and a duel color you like (meaning my color pair is blue and black, which is the Dimir guild!)

It basically means that when I buy cards I can stick in the color pie that I really like and lets me reuse really strong black and/or blue cards in all my decks.

Over time you'll just be able to use whatever colors you just have, this is just to start.