I spent quite a bit of time looking for a good visual tutorial for tinking and can't say that I found one. There must be one though and I just missed it.
Most people knit from the left hand needle (LH) onto the right hand (RH) needle . To tink you do just the opposite. You move stitches from the right needle to the left, unknitting them. The way I describe it is to point out that you don't do anything with the loop that goes over the RH needle. Look for the hole in the center of the stitch right under the RH needle. I usually like to pull up a little bit on the working yarn and maybe down a little on the fabric to "open" the hole up a little more (I knit Continental and for tinking I hold the yarn exactly the same way I do for regular knitting. I stick the LH needle right into the center of the stitch just below the RH needle, from the side facing you, nothing fancy, just straight in. Then you pull the RH needle to the right until the loop on the needle comes off, and tug ever so slightly on the working yarn until the stitch comes completely undone. You have now unknit one stitch and transfered one stitch to the LH needle. Repeat until where you want to be.
If the stitch is a purl, stick the LH needle into the stitch that is just below the loop on the RH needle too. The opening will be right below the "purl bump" that rides under the loop on the RH needle. Again just go head on into it, transferring it to the LH needle the same way you do a tink a knit stitch.
Some other points... if you have any yarn overs you just let them fall off as you come to them, they are no problem. Liz is right about the way to do K2tog. That's what I normally do too. Just had a brain freeze. There are other stitches you could encounter, but once you get the concept, you will know what to do with them.