If you are looking for transitions you might be thinking of using After Effects to edit video. AE is NOT a video editing app. It is a motion graphics and compositing application designed specifically to create effects, animations, and moving graphics that you cannot produce in an NLE like Premiere Pro. 

After Effects comes with a large collection of effects and you can do about 90% of what is possible in After Effects with nothing more than the standard set of effects, scripts, and extensions that come with After Effects. Many of the 3rd party effects that I use and most of the scripts that I have purchased just greatly simplify the workflow and allow me to accomplish what I need to accomplish in significantly less time with fewer layers and a faster render time. There is no danger in purchasing effects and scripts from known suppliers other than the fact that sometimes developers fall behind in keeping up with the changes in the core application so you have to wait for a while for the effects to work with your current version of AE.

More than 90% of all my compositions are a single shot that is under 7 seconds long because almost all of my videos are cut in the same style as movies. The average shot duration in feature films today is somewhere between 4 and 6 seconds. It is a rare occasion to see or use a transition in a feature film, television show, or even a music video so very few of my AE projects involve more than one shot. When I do put together a sequence it is never longer than a phrase or a sentence or two of dialogue. I do my editing in an NLE.

If you want to get a quick look at how to use After Effects efficiently take a look at the User Guide. To familiarize yourself with the UI open the Learn section of the Welcome Page or open the Learn Workspace in After Effects and spend 20 or 30 minutes figuring out the basics. Just spending those few minutes learning about the UI saves most new users several hours of frustration.  

Let us know if you need other help. 

In addition to shivangg's suggestion, could you take a look at this one, I know people who have used it and I have used it too and have had no issues.

Animation Composer 3

Hi there,

Welcome to the Adobe community!

We appreciate you writing in. Check out this article about the effects and animations that can be used and created in After Effects: https://helpx.adobe.com/after-effects/user-guide.html/after-effects/using/effects-animation-presets-overview.ug.html

Let us know if you have any questions.

Thanks,

Shivangi