Here's how to gather and dry kelp.
Kelp is rich in iodine, something many people don't get enough of.
Instead we ingest large quantities of nitrates and perchlorates, which can cause thyroid problems, especially in people with an iodine deficiency. The nitrates mostly come from preservatives in meat. The perchlorates mostly come from solid-fuel rockets and runoff from military installations, and are concentrated in the leaves of irrigated salad crops.
To learn more about these problems, here are some articles from google scholar.

WARNING
Kelp has a high iodine content. The iodine content varies greatly from one sample to the next.
Excessive iodine can aggravate thyroid problems. Tell your doctor what you're doing and don't over do it.

Step 1: Gather Kelp

Don't pick living kelp that's still anchored by its stem. The kelp has enough problems already from sea urchins chewing the anchors off, power boaters snagging them and tearing them off, etc etc.
Only gather kelp that's either drifting freely or has washed up on the beach. If there's current, here's how to tell if kelp is anchored without even touching it: If the "head" is pointing upstream, the kelp is anchored. If the "head" is pointing downstream, it's drifting freely.
If you still see a lot of the stem floating at high tide, the kelp is drifting. At low tide you'll see a lot of stem even on anchored kelp.

Here I am off the coast of Northern California. I found this bunch of kelp drifting in the current.
Put it in a bag or other closed container before you get to the beach, you don't want your kelp to get sandy.

Step 2: Rinse the Kelp

If you pick your kelp up off the beach, you'll need to rinse the sand off. The best place to do this is in the sea, right where you gather it. Fresh water makes the kelp really slimy so the sand sticks to it.
It's easier to wash the sand off in salt water than it is in fresh water.
If you want your dried kelp not to be so salty, rinsing in fresh water will do that.
I like mine salty.

Step 3: Dry the Kelp

Drying kelp is easy.
Just hang it anywhere there's some airflow and it will dry out.
You might think of hanging it on a clothesline, but...

Step 4: Built in Clothesline

Kelp has a built in clothesline!
If you find a long piece of kelp, you can just string the whole stem from tree to tree.
The Northwest Coast Natives used to use dried kelp stems as fishing line. If you need to tie two stems together, use a "granny knot". The "granny knot" looks like a square knot done wrong. It's usually a weak and unsafe knot, but is good for tying roots, vines, bark, and other stiff materials that will break if you bend them too far. I learned this from an Ojibway woman while helping to build a birch bark canoe.

Step 5: Dried!

Before long your kelp will be dried. It's amazing how thin and crispy it gets. Even the heads can shrink and turn into something you can bite and chew.
The white stuff on these heads are crystals of salt from the interior.
There are some spots on these leaves, they're eggs from some small sea animal, I eat those too.

Here's my non-scientific method to decide if I need to eat some kelp:
Caffeine stops having much of an affect on me.
I'm getting plenty of sleep, excercise, and sunlight.
I'm getting plenty of iron (anemia runs in my family).
Then I'll nibble a piece of kelp leaf each day for a few days, and usually the caffeine starts working just great!