FCP X doesn't use Plugins any longer, it uses specialized Motion 5 templates. So if you see folks on forums referring to effects, generators, titles, transitions, it's what we used to call plugins. Plugins are written using a specialized scripting program code, such as FXScript. With FCP X and Motion 5 us end users can do it all on our own, you just have to learn Motion, which is way easier than learning a programing language.
There is a Sharpen effect inside the Blur category. CHV's "Quartz Integration" has some much better sharpening effects for a good price. Be aware you can only sharpen so much, you can't make horrible footage perfect. Only improve it to a degree.
The larger developers will give you an "installer" that will place the effects in the correct places. They all go in [User Folder] > Movies > Motion Templates > and then into the appropriate folder there. Freebies you can find online (and there are tons of great ones, such as at fcp.co) should come with instructions on where to put what. It's not difficult to learn the system.
Motion 5, if you're really interested. Because all of this stuff comes to FCP X via Motion 5 and you can customize any of them, and create your own from scratch.