overstitch for clogs

[RuthK]

I'm making my first pair of felted clogs, and I'm not sure how to seam the soles - the pattern calls for doing an overstitch, but I'm not sure what that means. I looked at Amy's videos, and she has a note in the "finishing" section to avoid overstitching... any advice? Not only do I not know how to do it, I don't know if I should!