As someone already alluded to, Everest has a tourist-trap support system in place which effectively allows anyone with enough time and money to summit with only the briefest of orientations. To do this effectively, however, requires not only a high level of physical fitness, but also a significant amount of directly relevant experience climbing at high altitude.
If you are interested in training yourself to do this, you need to start training both for physical conditioning, and in climbing, self-rescue, team rescue and associated skills, and gradually develop your competency by completing ascents of successively greater technical difficulty.
If you do not already own a copy, purchase “Mountaineering: Freedom of the Hills” 7th Edition. This is the de facto standard text/reference book covering all aspects of mountaineering, and is a great place to start learning about the sport and associated skills and equipment. The book by itself is not sufficient to teach you anything, though, so you need to hook up with an experienced mentor who can teach you, or take a series of courses offered by a reputable operator.
Even if you have a course under your belt, understand that THERE IS NO SUBSTITUTE FOR EXPERIENCE. At best, such a course will give you the basic skills required in order to keep you out of trouble as you gain the majority of your knowledge through actually climbing.
I have been active in general mountaineering for fourteen years, winter alpine ascents for six years, and highly technical rock, ice and mixed climbs more recently. Every year I strive to do something more challenging, in order to practice the skills I have, and to increase my level of comfort when pushing my abilities. The 8000 meter peaks in the Nepal Himalaya are a lofty goal, but as yet, even if I could afford the trip, I don’t feel quite comfortable enough to attempt such an ascent without some more high-altitude and multiple-day expeditions under my belt. The more you learn, the more you realize how little you know.
Start with the book, though.