AmPro or otherwise Cooks of Reddit! I need advice on slow-cooking and seasoning a Roast!

I'm no cook. My abilities reach about as far as a box of Hamburger Helper. That being said, I'm trying to slow-cook a roast as a surprise for my husband (the cook for the family). I have no idea what seasonings (he has a ton!) to use. I have red potatoes, celery, carrots, and an onion. The roast itself is a beef arm shoulder roast. I have other things like bacon and other simple stuff...but I have no idea what to use...

How long should this take? What settings? ELI5, PLEASE!

Thanks in advance, and in return I will post any and all pics of before/after/French Bulldogs/Babies you want!