Never Played. Want to play. How do I start?

To be honest, if you are trying to learn the game to get to better ranks and not play casually then you should.
Learn all heroes to a degree, know what every ability does and try to remember how much damage they deal.

That thing should be your biggest priority in the start together with learning the maps really well, health pack positions & where you can go if someone is shooting your way etc.

Learn to differ shots, footsteps to know who is approaching you or who is where.
Try to learn tracking ultimate statuses on the enemy team, try to call out if someone is going to ult ( a good example of this would be a zarya running agressively towards your team at a point where she most likely has her ultimate. )
That way your team will be able to spread out, hopefully making her grav a waste.

Try to learn positioning really well, this can be done to a degree by watching streamers, thinking where people could approach from, shoot you from etc. have a reason why you position yourself where you do at any point.


Sorry if this text is a mess but I couldn't give you any more basic advice ;_;

tl:dr play more