Right-click on any clip on the timeline and select either Fade In or Fade Out.
If you'd like, you can learn a lot of these basics in my free 8 part Basic Training tutorial series at Premiere Elements support site Muvipix.com.
I am not 100% on your meaning of "I want to select a fading as standard." and your subsequence results "I followed the manual but the fading was not iserted into the timeline".
Is Time Stretch involved inn this footage to which you are trying to fade in and/or out? There are times when Time Stretched clip will not respond to the FadeIn FadeOut shortcuts, if that is what you are trying to use. If you are running into difficulties using these Timeline shortcuts, please check out my blog post on that topic
If that does ot help or apply to your situation, please go into more details on your goal for the task that you seek.