Beginner Question..When I want to make a 1-2minutes video and render them.

The only time you should use After Effects is when you cannot create the effect or the animation you want to create in Premiere Pro. More than 90% of my comps are one-shot under seven seconds long. Most of my comps have 10 to 20 layers and take several seconds a frame to render because I use AE for visual effects most of the time. If I want to create an animated video, animated graphics, or something similar my AE comps are never longer than a single sentence or a musical phrase. I complete the animation, render it, then do the final edit and sound mix in Premiere Pro. 

Editing a 1 or 2-minute video in After Effects can quickly turn into a logistical nightmare. I would not recommend it. 

Because you are new to After Effects start by opening the Learn Workspace and go through the self-guided getting started projects. It will take you 20 minutes. Then spend some time with the User Guide. It will save you days of fiddling and frustration if you get some good training on the basics before you start poling around and following a lot of poorly presented and inefficient tutorials enthusiasts constantly post on YouTube. 

I have had compositions in After Effects that were over 20 minutes long. I wouldn't recommend such things to a beginner, but sometimes it's necessary. USUALLY, I make short graphics in AE and then put them together in Premiere Pro, but as the others have said, it's up to you. Workflows are going to be different from person-to-person and, sometimes even with the same person, they are different project-to-project!

It depends. Premiere Pro is exactly what you need - it is software made for video editing so should be the best for combining several clips/scenes into one. But yo can also do that exact same thing with AE. 
In my opinion:
- if it is only 2-5 scenes/clips you can do that in AE or PPro
- if it is bigger editing project (10-20 or more scenes) - you should use PPro

It is up to you if you choose After Effects or Premiere Pro. The formats Youtube supports is as follows. You set one of them to render your animation.

https://support.google.com/youtube/troubleshooter/2888402?hl=en