You can use the Seaweeder Rake from shore, boat, or right from the dock. It can be used like a normal rake, drawn through the water towards you while dragging the teeth on the bottom if the water is not too deep.
For a farther reach you can gently throw the rake while hanging on to the included rope, the rake is weighted so that the head sinks to the bottom while the wooden handle floats slightly upright (this upright angle helps the teeth grab the water weeds). After throwing the rake wait a few seconds as it slowly sinks, and as the teeth contact the bottom slowly pull the rake to engage and retrieve the weeds.
The seaweed is intentionally brought back with the rake to be removed from the water. This is important because we don't want a lot of seaweed floating around, or even worse rerooting and spreading the problem over time.
Next, you have to remove the weeds from the rake after retrieval. To remove the weeds just hold the rake up and give it a shake, so the weeds fall away from the rake teeth. Sometimes for seaweed removal, it is best to rotate the rake 90 degrees and shake it, especially if the weeds are very long. Final cleaning usually has to be done by hand, pushing weeds off on an accumulated pile.
It might be a good idea to keep a smaller area clean, rather than trying to do too large of an area and making the job a real chore. Some people keep one side of their dock "weeded" for fishing and swimming and park their boats on the other side.
When you get used to how to use the rake, the task is rewarding and can become relaxing.