Is it compatible with your version of AE?
If so, I would try a new download. If that doesn't work, I would contact the author.
Videohove designers often include two project files with content they sell: one that uses third party plugins, and one that uses pre-rendered content.
Are you sure you're using the correct project file?
You can also directly message Videohive designers from their profiles within the Videohive website.
Like optical flare, and text. Where do I get these so I can use my video???
You buy them. Optical Flares is a commercial third-party plug-in for instance.