How do I paint stripes using different paint finishes?

You paint with the flattest of the finishes first, entire room. Once thoroughly dry, decide how wide you want the stripes to be (I did 12"). Measure the room and calculate so that you don't end up with a weird stripe at the end. This might require a slight modification of width.

Begin in one corner and measure the distance at the top, bottom, and twice in the middle for good measure. Tape off from ceiling to floor. If you have a line level, that will help you to get the tape straight and level.

Repeat taping ceiling to floor until the entire room is taped off.

Put a piece of tape in every other stripe to make sure you don't "get off" and paint 2 side by side or skip two.

Now paint with the glossier paint in every other stripe section that isn't marked with tape.

Once dry, remove tape.

I hope you have great leg muscles. I was sore for a couple of days. It's like doing a zillion squats.

Use a level , pencil and green frog tape. I've done it by painting the walls all one color in flat. Let dry for a good week, then taped off leaving what I wanted shiny and applied semi gloss aquathane. Very easy and fun. Do wide stripes so if room is not perfectly plum you won't notice. Have fun

There are some videos online that are helpful for planning. SW has one here https://www.sherwin-williams.com/homeowners/ask-sherwin-williams/painting/decorative-techniques/stripes-horizontal-and-vertical

I would not use a flat paint, unless it is a newer formulation that is washable. The sheens you choose may depend on exactly where you are painting, as well as whether or not there are imperfections in the wall surface (and the look you want). The more "perfect" the surface, the higher you can go toward the glossy "end" of the finish spectrum.

The previous owners of our home (unwittingly) did tone-on-tone for some touch-ups (possibly eggshell and satin), and they are (thankfully) hard to see. This is not the look you want, however! That being said, use 2 sheens that are quite different. For example, eggshell and semi-gloss.

You could get a quart of 2 or 3 sheens and a partial sheet of drywall and experiment (many times home improvement stores have drywall scraps you can pick up). For the base color (the one you will put on the entire wall), consider getting paint that has primer in it if you don't have primer on hand already.