Well, there's a number of different answers to that, and that will depend on a range of different circumstances. To begin with, your profile states no art at this time, so I would ask what you are refering to as an obi? The term is usually translated as "belt", but sash is probably more accurate.... and they come in many forms, from a "karate obi", to a wider "Iaido obi", to a formal obi for wearing with a kimono. Which do you have?
If it is an Iaido obi, do a google search for how to tie a Kaku obi; same for the rest. To let you know, though, there are a number of ways of tying Kaku obi (as well as the others), depending on the system and school involved. To get you started, though, here's one of my choices. It's in Italian, but can be translated, and has lot's of photos to guide you through:
http://www.katorishintoryu.it/Obi.htm
In terms of wearing the swords themselves, that will also change depending on the school (Ryu) in question, but a good rule is on the left hip for the Daito (long sword), and the Shoto/Wakizashi (short sword) across the front of your waist with the tsuka (handle) in front of your stomach. The Daito should be above the Shoto in the obi, so the saya (scabbard) of the Shoto is beneath the Daito's. Honestly, this isn't a great example, but it's the best I could find quickly:
http://www.toyamaryu.org/WearingKatana.htm
The tanto, if worn, would be worn in place of the Shoto. In fact, a Tanto (Knife, literally short blade/sword) could be classed as a Shoto (literally small sword) if worn with a Daito as a Daisho set. That could explain why you're not seeing both Wakizashi and Tanto worn with a Katana all at the same time.
These weapons are always worn on the left hip. There is no such thing as a left handed samurai (yes, I know that certain systems have left-handed kata, but that is the exception, not the rule, and it is usually for the element of surprise, as it is completely unexpected).