Take your shoulder pad and cut it into the right shape (a circle or whatever you prefer)
Now take your fabric (cotton fabrics work best in my opinion) and cut it into the same shape, maybe slightly larger
Sew the fabric onto the shouler pad. If you're not too familiar with using a sewing machine it might be a good idea to do this step by hand.
If you want your hat to look nice on the other side, too, you just have to cut out another piece of fabric and sew in onto the backside. If you have a piece of matching velvet or cord it would be a good idea to use it for this, those fabrics won't slip on your hair.
If you want a veil: cut a piece of tulle in the size you prefer and sew it onto the edge of your hat. It looks best if you gather it a bit for this.
Instead of tulle you can also use lace (like I did with the white/pale pink hat).
Now sew your bias tape around the edge of the whole hat. If you made a veil you can cover the seam with the bias tape so your hat looks nice and tidy in the end.
Now you can add more decoration to your hat. You could use some lace, ribbons, feathers, fabric roses... whatever you prefer.
In the end you only need to add some hair clips to the backside of your hat. You can sew them on, try to glue them on (haven't tried this yet, not too sure if it works...)
You could also use a hair comb or just add some lace that can be tied at the neck