I'm trying to do light leaks in after effects i have my own light leaks that i found but i would like to use the ones that After Effects has. I'm trying to achieve a slow moving light leak sort of like the video below. If anyone could help i would really appreciate it.
There are no built-in or canned light leak effects in After Effects. You could simulate them with some fiddling, but much easier to just download some light leak footage and overlay it on your footage/project using blending modes. There's free stuff you can download off youtube, for example. Or if you're happy to pay just a few dollars you can purchase some great stuff at stock sites like Videohive.