Embarassed to ask.

Like a kerf cut when you bend wood, it goes in.

Depends on what side the detail is printed on and what side is supposed to be visible. I know Eduard's instructions are usually pretty good at making it obvious. 

The best (cheapest) way to fold PE is by using a slightly dulled single edged razor (so you don't cut yourself) and a 6" machinist ruler. They cost a couple of bucks at a local hardware store. The ruler acts as a straight edge and the blade helps make an even bend. There are also folding devices by Small Shop etch mate and the hold n fold.

The groove is normally on the inside to make sure the fold is sharp.

https://www.zoro.com/westcott-ruler-6-inch-stainless-steel-10414/i/G3708144/?gclid=CKqoiPKhm9ICFZAjgQodrTEDQA&gclsrc=aw.ds

I some times get confused with it, even with Eduard instructions. Most of the time they go on the inside but tehre are exceptions. If i am not sure, i will fold the whole piece without gluing. If its wrong, then it usually can be folded back, but any more folding than that and it risks breaking.

Thanks folks, your info is very helpful. My thought was the crease went in so thank you for clarifying. Eduard does have fantastic instructions with thier sets but other in kit offerings sometimes aren't so clear. All y'all are great. Thank you

a friend showed me this technique for confusing bends or multiple bends. sketch out the part on a 3x5 card, cut it out and practice folding until you understand the direction and sequence of bending.  i have had instances where i made and destroyed 3 paper ones before getting it correct.

PS my first PE bending experince was the ammo box racks for the 1/35 MAS torpedo boat 20mm. after destroying 3 of the 6 i ended up making a jig and building all 6 from styrene.