If you're completely new to the idea I suggest the book With Each & Every Breath by Thanassiro Bikkhu. It's a Therevada Buddhist book but the breathing meditation instructions in it can be applied even if you want to ignore the other parts of the book.
The book explains their system and includes meditations. I can send you the audiobook and you can download the epub ebook from that Anna's archive link. Obviously also you can buy a hard copy.
I like the Healthy Minds program app more than other meditation apps because:
It's a curriculum so you aren't just handed a library to randomly choose, there's a set path.
It's completely free with no option to pay other than to donate.
There's a lot of speaker options and I like the speaker.
Someone else liked it: https://news.ycombinator.com/item?id=47710358
I'm working on a privacy-focused frontend for the Healthy Minds program because their app is very outdated and has a ton of tracking. You can use it on the web at https://getflourish.org. Completely vibe coded, very much not done, but it has the functionality to at least demo it. The Android app is a lot better but I haven't released it yet. The web version needs a ton of work it was just done in an hour based off the Android app and doesn't even format on desktop.
Please tell me how. I need to really really improve myself here. I used to be very good at being disciplined and focused, but being a parent and manager made me an ad-hoc reactive monkey that is always lagging behind with everything and not delivering on type, which I always did some time ago.