I do love this stuff.
Koi-Koi, my neighbour, brings me some from time to time, often together with some tajum, sea urchin roe, and they go well together.
They taste like salty little grapes, bursting in the mouth in the same way as caviare, but they're a lot cheaper.
This kind is my favourite. The branches are like little green Walt Disney toadstools.
To eat them, all you do is collect them straight from the sea. If you haven't got fresh sea water to rinse them in, use a little vinegar. But make sure you do wash them; a lot of tiny crabs and shrimp live in the bunches, and you don't want to chomp those as well.
I also featured another kind of lato at: Seaweeds as Food