Not much to say here.

Once you’ve reached this step you should already have everything printed in a pile of 5-page subgroups correctly arranged for folding. You only need to be careful when selecting the pages that should go in each booklet.

I do the folding manually. Just take the pages, align them properly so that none shows over the others and fold them carefully. You’ll need the best possible alignment you can get since the final look of the book depends on it. I usually take the group and have the opposing shorter sides of the sheets make contact before applying any pressure. If you’ve ever done Origami you’ll know that otherwise you’ll end up with misaligned borders.

It has no complication at all, but you have to be extremely careful each time you fold a booklet or the sides of your book will end up being irregular. My folding is never perfect, but it gets close. Anyway the side opposing the spine of the book will inevitably have an irregular aspect since the innermost pages of a booklet will protrude over those at the outer part. Don’t worry about these triangle-like alignments. We’ll take care of them when we get to the trimming part. For now you have to make sure the lower and upper sides of your book are as aligned as possible.