Stain & polyurathane

stain...a rag

polyurethane...roller, see website below

https://www.hunker.com/12500283/how-to-roll-on-polyurethane

https://www.popularwoodworking.com/techniques/finishing/finishing-for-first-timers

After sanding, stain with a soft cotton rag (my go-to is socks - I keep a large bin in my workshop of mismatched, old socks). Start with very light coats - do several, letting each coat dry in between each one. Light sanding can be done in between with high grit sand paper or steel wool. Then apply a light coat of polyurethene - again you can use I usually use a rag for even coverage. Do another coat the same way. If you get bubbles or streaks, lightly sand again or use steel wool to smooth.

They make mirror finish rollers. I got mine at a Menard's store and had the best luck with it.

I would suggest a high-density foam roller.

You can use a brush or lint free cloth to apply the stain. Use a foam roller, foam brush, or spray to apply the polyurethane. At least three coats of a water based polyurethane lightly sanding in between coats. I like to use a Red Scotch Brite Pad rather than sandpaper.

I love a Minwax product called “pour on poly”. Totally goof proof!!