I have a round electrical wooden spool I want to stain it, how do I do

They are usually just raw wood, so it should be easy to stain. Just check it out to be sure there's not major splinters on it that someone might hurt themselves on, then choose the color of stain you want to use. A home improvement store such as Home Depot, Lowes, or another will have a wide variety for you to make a choice. There may be an "outdoor" stain available if you plan to keep the spool outside in the weather. If you do keep it outside, I'd recommend spray or painting with a clear marine type finish to stave off the elements of weather. The stain could be applied with a sponge or brush or even a soft cloth, then wipe off with a clean cloth. You can build layers of stain to get it the "depth" of color you like. I'm assuming you were asking how to go about staining it. Bet it will turn out great!

It’s most likely pine...a soft wood. Or an oak a hard wood.Try a dot of the stain in a not so readily seen place. See how it looks. You may need a wood conditioner for it If it’s pine It helps keep the color consistent. Then put your stain in place. Oak not so much.

Just like any other wood. Sand, stain, seal!

I recommend using tung oil on bare wood before staining. It will preseal the wood and keep the stain uniform