I have been meditating more-or-less daily for > 10 years. It is a very useful practice, depending on your goals. It's good to ask yourself why you want to meditate, so you can tell if it's working or not. It's a bit of a chicken-and-egg problem if you don't know what other people get out of it, though, so here are a few things that I have been aiming for, and how well it worked for me.

Nibbana / Cessation

Many practitioners have spoken of a mental state where thoughts cease, and time seems to pass in an instant. It is supposed to be a transformative experience according to most traditions. You are a wiser, calmer and more caring person from that point forward.

I was seeking this for a long time, and I say it's bullshit. (Or maybe just not possible without becoming a monk & practicing all day every day, which is the same thing when someone tells you it's posslble to get there in 30-60 minutes per day.)

Feel happier / less anxious

Anxiety and depression are things a lot of people with ADHD feel. I have found that daily practice really does help with this. Breath meditation improved my mood and gave me a bit more peace, but a "metta" style (I mostly follow a practice called TWIM) works really well for me.

Make better decisions

You wouldn't think that this would come from just sitting there focusing on your breath (or in the case of metta/TWIM, on a warm, happy feeling), but it does for me. I think that the reason I tend to eat better, exercise more, etc, come from a better understanding of my own mind. There is so much noise in most people's minds (and probably more than average in our ADHD minds), that sitting down to meditate feels like your brain suddenly went into overdrive & you can't focus on anything. The truth is that meditation lets you notice that your mind is always like this. Realizing this (the constant state of distraction) helps me trust my gut reactions less, and rely on logic more.

Improve your focus

Meditation helped me build more focus. Even though you can't really keep your attention on the meditation object for more than a few seconds at a time, constantly (and gently - it takes a long time to learn to be more gentle) directing it back over & over again "builds that muscle". Meaning, I'm able to redirect my attention like non-ADHD people seem to, more of the time.

Caveats

Maybe I can save you a bit of struggle, or maybe you need to suffer through it yourself. In any case, here is some additional advice, if you want to pursue this:

• Don't worry about the mystical parts of meditation, unless you find that motivating. It can be purely secular & still be effective (and maybe even "spiritual").
• Don't try to follow the standard advice for duration. I'd suggest starting VERY small / slow. Just 1-5m per day. If you haven't meditated, it will seem like you're trying to herd cats with even that much time, at first. I was doing 45-60m/day for over a year, and it was unpleasant. I do 15-30m per day now (most days, 15-20), and I get a lot more benefit from it because it's relaxing.
• Do follow the advice on frequency. This is something best done every day. Put it on your calendar until it's a habit.
• Smile while you do it. You don't have to put on a huge grin (though I often do - it just feels natural now).
• Don't worry if you forget a day, or a week, or a month. It will still be available to you if/when you come back to it.
• Get a random reminder timer (I use an android one called "Randomly Remind Me") to ping you a few times per day, and do a mini meditation. I find that I can get MUCH calmer with just 3 slow breaths or a reminder to do "6 R's" (see TWIM, above) for 30 sec.

Good luck!