Bob,
Assuming you're not interested in backpacking... and you've already said you're not... then these are the things you should do if your time in Yosemite is limited to 1 to 3 days.
If your time is REALLY short, ride the free shuttle or the tour bus around the valley loop a couple of times, then drive the 15 miles (or so) to Glacier Point. If you have 3 hours more, do the Sentinel Dome hike - which begins RELATIVELY close to the Glacier Point summit parking lot. If you have still more time, hit everything else on this list depending on what sounds cool to you.
Unless your flight is tomorrow, take the time to do a little internet research of these recommendations. It will be worth the while to know what you want to see before you arrive. Yosemite is a big place - larger than Rhode Island, as I recall. Driving from one end of the park to the other will take a couple of hours - so plan accordingly.
Glacier Point. The #1 “must do” item, and you can drive all the way to it from the valley floor. You'll need at least 2.5 hours to get to it, do your gawking, and return to the valley floor. It's a slow, windy road, and you'll invariably get stuck behind some Japanese tourist in a 40 foot motorhome, doing 10 mph on 35 mph roads and not pulling over.
From Glacier Point, you'll see this: http://www.360cities.net/image/harf-dome-from-glacier-point-yosemite-usa#16.20,0.40,40.0
On the way back from the Glacier Point drive, there’s a pulloff on the right (easily missed) that is a starting point for the Sentinel Dome walk. It’s an easy hike of about one mile each direction, with a few hundred yards uphill once you’re almost there. FANTASTIC 360 degree view.
Bridal Veil Falls (go up the road further to Valley View or Tunnel View (multiple names)) - the pullout right before the tunnel on Highway 41. Great vista point. It’s a classic. Looking at Bridal Veil, Leaning Tower, El Capitan, etc.
Mirror Lake isn’t too great anymore. It used to be better, but they aren’t pumping the sediment out anymore. (So don’t believe other people who tell you it’s awesome. They haven’t seen it lately.)
2 hour hike, the John Muir trail starting at the Happy Isles shuttle stop. Go at least to the first bridge for a view of Vernal Falls. That’s about an hour. You’ll spend some time gawking. Then the hike back is faster and easier.)
Park at Yosemite Village Store and hop on the shuttle. Take the free shuttle around the valley… just to take in the loop. Or pay for the open air tram and a ranger will take you around the valley.
Olmstead Point (on the way to Tuolumne Meadows.) See the back side of Half Dome, Other domes, Cloud’s Rest, Tenaya Lake.) Vista point. No hike required.
Tuolumne Meadows. From Yosemite Valley, this is a pretty long drive… my recollection is that it takes an hour or so. But it’s a beautiful drive.
Mono Lake – 20 miles or so beyond Tuolumne Meadows. Outside of the park. Worth it to see the tufa towers emerging from the lake and the volcanic residue, and cool cinder cones (decent sized hills) you can climb. Worth doing since it’s a COOL* climb. Tons of volcanic ash, obsidion and pumice boulders. When hiking along the lake, use care whenever you pick anything up. Unless things have changed, there's a scorpion under every single softball-sized or larger rock!
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