I agree with Frisco_Roadrunner and I had to laugh at the 'don't look at photos' part.
September is a fabulous time to visit. I hope you have several days available. This would be my idea of an ideal first visit:
Day 1 - leave Las Vegas really early. Drive thru DVNP and enjoy as much as possible, especially quick viewpoints. Continue out the Panamint Entrance, taking in views from that side.
Night 1 - Lone Pine
Day 2 - Eastern Sierra ... so many options. Read ideas here: tripadvisor.com/Travel-g28926-c182361
Night 2 - maybe Tuolumne Meadows lodge if you like tent cabins and if it's still open, or maybe Lee Vining or June Lakes
Day 3 - leisurely drive through Tuolumne Meadows, stopping for walks or hikes, stopping again at Olmsted Point for views. Continue to Yosemite Valley and spend some time. Drive up to Glacier Point for sunset.
Night 3 - Yosemite Valley
Day 4 - more time in Yosemite Valley, and then maybe a visit to nearby small Tuolumne Grove of Giant Sequoias or larger further Mariposa Grove of Giant Sequoias. Drive 4+ hrs to San Francisco.
With an additional day, you could spend more time in Yosemite Valley & Glacier Point ... maybe a longer visit to a grove of Giant Sequoias.
With only 3 days & 2 nights, you could spend the first night in 'western' Lone Pine or Bishop and the second night in Yosemite Valley.
Lodging reservations for Yosemite are absolutely required. Read the Top Questions about Yosemite in the upper right of the Yosemite forum page for suggestions including the link for the official concessionaire and private property options.