In way over my head in Illustrator

My boss handed me Illustrator and asked me to create print ready artwork with bleed marks for #10 window envolpe So we can have them printed with our logo and address.  I don't even know where to start!!

I have opened some existing AI files we have but they are all 8.5 x 11 and honestly I couldn't learn anything from them.

I'm not asking for someone to hold my hand.  I just need to be pointed in the right direction.  Surely it can't be that difficult.  It's only a little text and a jpg file all in one color.  My art experience lies in CAD drawings and a little in Actobat.