What Sue says is very helpful. When finishing the sleeve work the last round to 4 or 5 before your beginning of round marker. Then bind off the 8 or 10 right across the beginning of a new round. Stop right there. Now you take your long circular and using it, knit the rest of the way around the sleeve you are finishing.
When you get back to the bound off stitches you will hold the sweater body up like Sue pictured (Take time to hold the whole sweater together with the body and the sleeves pointing in the right directions to make a sweater, imaging the yoke being where the parts come together. That will help you picture what must happen to put the parts together to form the sweater.) and begin to knit across the front of the sweater between the two sets of bound off stitches at the underarms. Put in all the purls, place markers etc. where they tell you to. When you get done with the front section you then work around the other sleeve. Lastly you work across the back of the sweater.
Sue's illustration of the "oOo" is good. Picture the 3 circles actually touching each other (those are the underarms) and you will knit all around the outside of the three circles.
I have found that sometimes when they say to use a long circular needle for this type of yoke that it is still difficult to actually do it all on one needle like they say. Sometimes I have found 2 or 3 circular needles to be needed to make it easier. But remember you want the result to be one continuous circle of knitting (like it was all on one needle, if you can't actually get that to work at this point) around the outside edge of a sleeve, across the front of the body, then the outside edge of the other sleeve, and on around the back of the body. After you do a few rounds you can usually get it to work on one needle and can ditch the extra ones you may have decided to add.
I hope between reading Sue's post and mine you can get this done.