Yep, the raglan "seams" are the triangle-looking thingies! I didn't look at the pattern (i am a member of too many places already! I don't need more temptation!), BUT, here are your options:
If the stitches are live (on holders) you can attach the top ofthe sleeve to the shoulder with a 3 needle bind off. This is not an invisible seam, but that might not matter since the raglan shaping will be obvious anyway (that's the point!). It might feel funny though... like a lump along the seam.
If the stitches are live (on holders) you could graft them together. This is also called kitchener stitch, and it sounds tricky, but it's actually easy once you get the pattern down. This makes an invisible/non-lumpy seam.
If the edges are finished, you can use mattress stitch, which creates an invisible, non-lumpy seam too.
Either of these techniques might require a bit of fudging, if you don't have the same number of stitches for the shoulder as the top of the sleeve.
Amy has videos for all three of these techniques, on the More Basic Techniques page, about halfway down under "Seaming"
I think that some knitters differ on this, but my advice would be to sew the side seams first (using mattress stitch, since it's invisible), and then put in the sleeves. The pattern might say something different (and Ingrid, who is super-knitter, might have different, better, or different and better advice ).
I haven't actually done this: the one raglan sweater I've done is a cardigan which was knit top-down, and the raglan shaping/seaming was done in one step. BUT, this is easy, and I know you can do it! Good luck