Let me know if it doesn't work out (not sure what skill level this is good for).
Also, post any questions in the comments, and I'll be happy to answer them!
First, put the two outer pieces together with the right sides facing. Sew the two outer edges (since I used a long rectangle, I only needed to sew one edge). No need to finish the edges since they'll be enclosed once it's lined.
Fold the bottom ruffle strip in half widthwise and iron. Pleat it, pinning the pleats in place.
The strip should fit snugly inside the bottom opening, where you'll want to line it up with the raw edges hanging out a little bit (to make sure that you won't have any edges sticking out of the right side of your bag on the outside).
Put the two lining pieces together, right sides facing, and sew around the sides and bottom. Clip the bottom corners so that it'll lay cleaner on the inside.
For the strap, sew a tube then turn it inside out. Iron it flat, and topstitch down both long sides.
This is where a little more attention is required. Line up the short ends of the straps with the top edge of the bag. Make sure to line them up with the exact sides of the bag. Pin.
Line up the top edges of the lining and the outside. Make sure the strap ends are sandwiched in between. Also make sure the straps are lined up with the exact sides of the lining.
Sew a straight stitch around the top edge, leaving a few inches open for turning.
Topstitch around the edge of the top of the bag. When you get to the opening, make sure that you aren't stitching below the open edge.
Now for the embellishment. If you have multiple strips, sew the ends together to make one long one. Fold your strip in half widthwise and sew closed. You don't have to turn it inside out, because you'll be hiding them. You also don't need to finish the raw edges if you're hot gluing, because you can seal all the edges down with the glue.
If you need to, draw a circle on your bag. I just eyeballed. Run a line of hot glue 1/4 of the circle, and press the raw edge of your strip into it, about an inch at a time. Every inch, make a small pleat and turn your strip to follow the glue line.
Continue until your circle is done, then run another line of glue along the inside of the circle, as far in a necessary to expand your flower but still hide your raw edge. Continue the flower in this way until you're done.
Tuck the end edge under and glue into place. Dab an adequate amount of hot glue in the center of the flower and stick on a bit of flair. Please be more careful with your hot glue than I was. I got a little messy! Add a closure to the bag top if you want, and you're done!