Putting on a kimono and especially tieing the obi is an art that has to be learned in courses or by books and is almost as difficult to achieve without another person's help as putting on a back-lacing corset. I can only give a limited overview over female kimono - for men it isn't half as complicated anyway.
Putting on a yukata is much easier, for it requires neither undergarment nor any of the other accessories which are hard to get outside Japan. However, if the yukata is worn as a proper street dress and not as a dressing gown, there's a special kind of obi tie (see pic). Yukata are worn in summer without tabi and with geta.
For wearing a kimono with the obi tied "drum style", the most usual style for formal dress for anyone but the very young girls and women, you will need the following items beside the kimono:
Turn to the glossary for an idea of what a new outfit would cost and what the items look like. If you buy used items, you can get away with roughly 15,000 yen.
Put on the tabi and the undergarment, folding the left front flap over the right. Always left over right, except for funerals! When the undergarment sits straight, tie it with a thin sash or ribbon. Now put on the kimono and smooth out the sleeves of the undergarment within the kimono sleeves.
Open the kimono wide and pull it up until the hem is at ankle height (a kimono is longer than the wearer), then close it, left over right. The end of the collar should be near the hip bone, the edge below hanging vertically. The hem of the right flap must not be seen below that of the left. Use another sash to fix it so that the surplus in length bulges above it. Smooth it down over the sash, arranging the collar so that a bit of the undergarment shows.
Now the obi. A series of sketches will be offered soon, hopefully. Place the narrow end of the obi over your right shoulder from behind, so that the end is just below breast level. The side where the two layers have been sewn together should face right. With the left hand, reach behind you and pull the other end to the front, placing it horizontally over the narrow end, thus fixig it. Now you have the right hand free to pull the long end further round, around the back and to the left. Take the long end into your left hand, carefully pull out the short end with the right, and pull tight on both ends. See to it that the surplus of kimono length that you had smoothed down shows as a neat horizontal fold below the obi or, if there wasn't that much surplus, doesn't show at all.
Let the short end fall behind you so that it hangs at the right side, and lead the long end round to the back once more, this time placing the piece of cardboard under it. It will ensure that the obi sits straight over your stomach. Now the triangle created by the transition from the narrow to the wide portion of the obi should be at your centre back. Fold it so that the wide end faces upwards and fix it just above the obi using the odaiko. Reach down with both hands, grab each edge of the wide end, and pull it vertically upwards until the fold touches the odaiko. Adjust it so that the very end sticks out about a hand's width under the "drum" thus created. Hold it in place with your left hand, grab the narrow end you'd let fall behind you with the right and put that through the drum. If it sticks out too much on the left side, fold it back to the right. Now fix it with the obi-jime in the middle of the obi, and hide the odaiko under a decorative sash the surplus ends of which are stuffed into the obi.
Phew! Done. Now the zôri, and you're ready to go. Speaking of going: The kimono is rather tight around the knees, so when walking you should keep your knees close together. In conjuction with the footwear, the effect will be a shuffling walk that's considered elegant in Japan. The elegant stance when standing still is with the feet close together, the toes turned slightly inward.