I took some photos back in 2008...on how this joining of the body and the arms works. Anyway, I still have the photos...and I hope this photo set also helps you, bearing in mind...that I knit in-the-round with the Right Side on the inside of the 'tube', not on the outside...but the photos still serve.
Here is the 'body' of the sweater, ready for sleeves to be "attached/joined" and the yoke to be created. The turquoise blue 'waste yarn' are my 18st "on hold" for later 'seaming' to the sleeve's 18st on hold, forming the armpit seam. This isn't done until the yoke is all knit up.
Here is one of the sleeves, ready to be joined to the body. Notice, the 18st 'held on waste yarn'. They are the armpit stitches, to be seamed to the body's 18st 'held on waste yarn', after yoke is done.
I clipped the sleeve to the body, everything lined up...sleeve 18st on waste yarn to the body 18st on waste yarn...later on, after the yoke is all knit up...you will join those 18st together and they will be the armpit seam.
Notice, I used one long circular and ran it around through all of the body stitches and the sleeve stitches.
Now I'm ready to begin knitting round and round...on the outer perimeter of the sweater, forming the yoke.
I like to knit with the RS on the inside, and it makes no difference to the knitting. I could just as easily turn the work inside out at this point. I like to keep the RS on the inside, protecting it.