I have a sliiiiight problem. Whenever I try and make liveries in fs2020 I need a texture to paint on the plane. I make the texture (white), and it is all good. But then the texture applies to every. single. object. in blender. So everything is white expect for the part I painted. Obviously airplanes aren't full white so I was wondering if someone had a work around or a fix to this. Thanks in advance

I'm not sure, but if everything except the part you painted is white, maybe you're making an alpha mask. Or opacity map if you like. 
I haven't made liveries in ages, so someone else might have a better explanation. 

I just make a "Base Color" and I just applie to, well not everything. The prop, engine, wheel, etc. 

Suggest you have a look at some of the YouTube video tutorials on painting with Blender.  A very brief summary though:

Easiest thing is to make a template with your livery colours in a paint program and save it as a png file.  Paint this onto the model in Blender using x-symmetry so you paint both sides the same, ensuring each object is painted before you change to another png image.  Save the texture files individually.  Then for each side make a template with the images and text, the rest of the image being transparent so you can paint over your livery colours.  Paint each side with the text and images, ensuring for each object that you do not have x-symmetry on, and when finished save the texture files again.  Then in turn then apply each of the texture files to the relevant background image from your paint kit, set up the livery package and install into MSFS.

 

https://youtu.be/3atVWEEITQ0