I don't think I can ELI5 this one, but here's an ELI15 version: Wasp genitals don't actually resemble human ones very much, but if they did, these wasps would have had - not only a set of "labia majora" that would in itself be unlike anything else now living or yet known - but 'labia' also fringed with stiff, Venus-flytrap-like hairs that the wasp might use to pin her reproductive host 'prey' (probably a caterpillar or beetle, or an arachnid, or like that) for long enough to oviposit, before releasing the host to go about a life now shortened by its parasitic passenger. While parasitoid oviposition is extremely ordinary (in fact, by far the most common reproductive habit by species count) in wasps, these 'Venus flytrap,' 'labioid' accessory structures are almost totally novel among not just wasps but all insects.

Longer, more complicated first draft: The final two segments of the wasp's abdomen are modified into something totally unknown in modern hymenopterans ~(ants, bees, wasps) and most closely analogous in modern arthropods, though not remotely homologous, to something like the dragonfly's reproductive claspers. Different fossilized adults show one of these organs articulates with respect to the other, presumably in a way that can be differentiated from the distortion often typical of the fossilization process, which would suggest the animal had volitional control over what would otherwise, after all, obstruct her quite severely in the use of her genitals. (Exoskeletal animals' muscles insert into their sclerites a lot like how ours attach to our bones, and just as with our bones, the skeletal structures that have evolved to give mechanical leverage to that muscle attachment may survive to offer insight into how the organs might have worked, on largely mechanical principles similar to how an idler implies a shaft and a belt.)

The surmise with regard to functionality, which is all it could be on so little evidence, is that with the gross (fossilized) anatomy resembling that of a Venus flytrap to the extent of bearing similar marginal setae (hairs around the border), this anatomy served the reproductive purpose of temporarily immobilizing prey during oviposition, which would occur via closely colocated genital organs which, though I didn't them see discussed in the paper and may not have been sufficiently preserved in fossilization, would likely have been similar to a more basal ('primitive' though the term is inexact, properly more similar to an older common ancestor) version of the ovipositor that modern parasitoid wasps have.

It isn't an unreasonable surmise that these newly identified organs would be used in that way, though I expect if I had yet read further into the paper I would find some consideration of possible reproductive accessory use, such as engaging a male wasp somehow during mating, or helping deny access to unwanted suitors. I'd like to hope for the close analysis of muscle articulations I suggested earlier, but for fossils from 100Mya, it's probably a marvel we have so many specimens of one species from even so long populous and cosmopolitan a clade as the Hymenoptera.