What are the 1st steps in selling a oil painting, when I am ready to do so.

You could find some places that exhibit local artists and ask if you can do a showing.
You can make a website with your art and advertise your site.
Maybe place an ad on Craigslist.

Is this oil painting something that you have painted, or the work of someone else? Thanks!

Whether your work art work or a painting by someone else that you own and want to part with, Ebay is always an option.

If you are the artist, I would find a printer who does "Giclee" prints, have your work scanned so you can make prints later if you want to sell those, then, like NOhelp4u suggested, find art shows that would allow you to show your work.

I do like the idea, that if you are the artist, to make more images in different formats so that the original work can be marketed in more than one way.