Exercise is a big part of my life now but I'm 7 years into my "journey." Originally in 2013, I went from 96kg to 78kg in 6 months purely on diet with no additional exercise (even though I knew I should have been adding in Exercise.) I relapsed in 2015 to 89kg and began 2016 redoubling efforts on my diet and then a couple of months later we had a Wellness program at work with exercise classes and everything suddenly clicked into place fitness-wise.
Suffice to say, I am pretty deep down the rabbit hole that
@Scary_Turtle mentioned.
In terms of weight loss, diet will achieve 80% of your potential with no exercise and if you have a lot of weight to lose, diet will be more effective and most likely less risky than focusing on exercise alone but the two always complement each other.
Community is also incredibly powerful when it comes to this sort of lifestyle change -whether it's a class, a club, online forum or whatever, your journey is richer and stronger when you walk your road with, and for others.