Let me take a crack at it.
[COLOR="Blue"]With RS facing, work across left front sts, place 68 sleeve sts on waste yarn, removing markers, [/COLOR] -- Do exactly what they're telling you: Work across the left front, then place the next 68 sts on waste yarn, removing any markers. These 68 sts are for your left sleeve.
[COLOR="blue"]use the backwark loop method to CO 4 sts for underarm,[/COLOR] -- Cast on 4 sts on to your working (i.e., right) needle for the underarm. When you cast on additional sts, you always cast on to your working needle.
[COLOR="blue"]pm for beg of rnd, CO 4 more sts as before[/COLOR] -- Place a marker to show the beginning of your round, then cast on 4 more sts on to the right needle just like you did before.
[COLOR="blue"]k92 back sts[/COLOR] -- Knit the next 92 sts which will be the back of your garment. That's what they mean by "back sts" -- sts that form the back. It doesn't refer to how you work them, just to the garment section they will form.
[COLOR="blue"]place next 68 sts on waste yarn for other sleeve, removing markers[/COLOR] -- Put the next 68 sts on waste yarn for your right sleeve, again removing any markers.
[COLOR="blue"]CO 4 sts as before, pm, CO 4 more sts as before[/COLOR] -- Cast on 4 sts, place a marker, then cast on 4 more. This should be a mirror image of your left side.
[COLOR="blue"]k31 front sts, CO 30 sts for center front[/COLOR] -- At this point, unfortunately, I would need to see the pattern or at least a picture of the garment in order to figure out what they want you to do for sure. However, if the instructions are correct as you have typed them, you simply knit the next 31 sts for your front, then cast on 30 more sts for the center front.
At the end of it all, you should have a total of 200 sts on your needles with an additional 68 sts on waste yarn for the left sleeve and 68 sts for the right sleeve.
Looking back over this response, it certainly seems long winded and I apologize. However, I thought it better to break things down as much as possible to make sure I answered all of your questions.
I hope this helps, but if not, come on back and I'm sure you'll find someone who can answer your questions.