Best place to practice just clipping in and out, to get the feel of SPD's or any other clipless pedals for the novice user, is your home's hallway. Yep, just get into your hallway, mount your bike, and then just practice clipping in and out to your heart's content without any fear of falling over....the close walls will give that security. But this practice is important to get that "feel" of what the pedal and shoe feel like when you're in the right position to clip in, and what the release move feels like. Naturally, at first, which you've probably experience already, the "feel" is horrible. This will pass, though. I know right now the SPD shoes feel like you have boards of wood strapped to your feet and "How the heck does anyone feel where your foot is and where the clip in spot is?" The "feel" will come with time....just get used to the fact that you're going to fumble with clipping in right now as you develop a feel for the cleat/pedal interface....it will come.
But, on your first ride or two, count on forgetting to unclip when you come to a stop.....it's not a natural action at all and must be learned. After a few days of use, though, and the clipping in and out action will become second nature. And when you fall at a stop (tip over to the side), which you invariably will, at least it'll be a slow fall and easily controlled with one hand to break your fall.
Couple of other hints......first, pick one foot to be your down foot at stops and one foot to be your on-pedal, ready to go foot....and then be consistent about it. That'll just make commuting life much easier. When you're commuting, you'll rarely have to use both feet to balance yourself....instead, you'll find that just removing one foot from its pedal and using that one for balancing at a stop sign or light or whatever is about all you need to do. Doing it this way also gives you the ability to take off quickly without having to fumble around with trying to clip into both pedals from a standing start.
Second.....about taking off from a stop when you've unclipped one foot.....don't make the novice mistake of trying to clip in immediately when the pedal first comes up when you have given the bike one pedal stroke. You're moving extremely slowly at that point and your balance is at its worst......not to mention you're probably either in traffic or trying to get across a street with traffic moving on it. Instead, just slap your unclipped foot onto the pedal and just pedal a few strokes unclipped.....then, once you get a little speed up and you're moving along with good balance, coast for a second and clip your foot into the pedal and continue on. Many, many novice SPD/clipless users make the mistake of trying to clip in too soon with the inevitable crash happening because they're fumbling with the unclipped foot trying to find the pedal's and shoes' cleat clip in mating point. Their speed drops so much that they have to either stop or tip over.....because panic frustration are setting in. Just pedla off and clip in when you've gotten some good forward momentum built up. It'll make your life a lot easier. As you get more experienced, the speed by which you clip in will get faster, but even very experienced commuters who use clipless pedals will clip in after they get across the street or after a few pedal strokes.
Third, SPD pedals have, typically, a tension control on them. The tension control is to make the mechanism on the pedal that holds the shoe's cleat easier or harder to pop out of them......very aggressive riding will require a higher tension than just flat land riding......but as a rookie with SPD's, I'd suggest you set the tension to the looser end of the scale. While this may make it easy to unclip when pedaling, it will also make it easy to snatch your foot straight off the pedal in an emergency situation without having to do the heel kick move to release from the pedal. As you get more experienced, begin to tighten the tension so you can put more force into pulling up on your pedaling stroke.....another advantage of clipless pedals. You can pull up as well as push down in pedaling....or even one foot pedal, always good for a laugh or stare from the unwashed non-riders out there as you pedal by with one foot hanging loose....
Good luck....and don't get discouraged. There is a learning curve to clipless pedals. Endure it and you'll never want to ride a bicycle without them....they're so much more efficient.
Oh, and Dirigible, I did look at the linked pedals you showed.....and I'm surprised Shimano is still making them today. They're about the worst abomination of SPD pedals on the market and very few people actually ever buy them, much less use them.....as I notice you are included in this group, too, with your "I think I've got a set hanging around my bike shed somewhere. I didn't use them for long and could sell them pretty cheap if you're interested and I can find them," comment. I think that pretty much sums up what almost everyone that actually falls for the look and promise of them ends up doing with them.....taking them off, ditching them in the garage or closet, and either returning to pure platforms or pure SPD's instead of those bastard pedals. And one can ride SPD's with tennis shoes if one has to.....wouldn't do it for long distances myself, but have done it for a quick trip to the corner store.