How to create a transparent background on ms paint?

To do this at first on the toolbar, go to the “Image”  then click the  right below “Select”. Choose the “Free-form selection” tool instead of “Rectangular selection”. Next, make sure to check the option for “Transparent Selection”.
then 
Using the free-form selection tool, carefully trace the object that you want to place on top of another image. Make sure to exclude all of the elements and colors that you do not want to see. When tracing, just left-click and hold your mouse. Do not release until you’re done.
after that,

 you will notice that the traced portion of your image will be enclosed inside a rectangular box (selection box). Just right-click on any portion inside the box then select “Cut”. This action will cut your traced object so you can finally transfer and place it on top of another image.

next,Moving on, just discard your first image and open another image. After which, enter “Ctrl + V” on your keyboard or simply click “Paste”. This will paste the image that you cropped from the first image on your second image.

Move the image to your desired position and that’s it!
Done!!!
hope this helps