Hello, Im new here so Im sorry if I do anything wrong 
I wondered how I can achieve such vocals in audacity. Is it possible? And if yes, how to do it?
Like this:
https://www.youtube.com/watch?v=WTsmIbNku5g
Or also like this:
https://www.youtube.com/watch?v=I-7Nnf3x0-c
If its too hard to explain easily, I would also love maybe articles or videos that give me the understanding of it ^^
Thank you! 
Step 1. Find someone with a good singing voice with an appropriate character / timbre to the voice.
Step 2. Write / arrange / record the instrumental tracks.
Step 3. Record vocals
Step 4. Apply a shed load of effects to taste.
The two samples you gave have little in common other than the “dreamy” vocal style and over indulgence of effects.
The hardest part will be finding someone that can sing like that (unless you can yourself).
You can change the speed of your recording, faster makes it like a chipmunk, and slower makes it deep.