Most people start with the letters

I've just bought a Tusitala Stevenson. It had been sitting in the window of the second hand bookshop down the road for a couple of weeks. I've been curious about some of RLS's more obscure works for some time, so it seemed a good omen. I find myself briefly in another world. "Most people start with the letters" says the book shop man rather cryptically. I must look blank, because he explains that the volumes of letters are the most awkward to find, therefore if you care about getting a uniform edition, it's best to acquire them first, then look for matching versions of the more commonly found volumes. Of course. I don't like to mention that I am no bibliophile and only want to read them.