For making these bracelets we just need bead strings or jute strings and stick the shells onto them with the hot glue gun and simply tie a knot after wearing or we can also attach hooks. The hooks are optional and can give your piece a more finished look as compared to being without hooks.
Seashell Necklace:

Image: youtube
Seashell Pink Tassel Bracelet:

Image: pinterest
Beach Shell Hair Pins:

Image: polkadotchair, pinterest
Netted Stone Macrame Friendship Bracelet:

Image: cutoutandkeep
Shell Bracelets:

Image: saturatelife
Seashell Beaded Headband:

Image: howdidyoumakethis
Shell Necklace: DIY

Image: beadinggem, beadinggem
Sea Shell Earrings:

Image: instructables
Seashell Flower Necklace:

Image: momsandcrafters, etsy
Shell Crown Tutorial:

Image: youtube