There’s a lot of good information about leveling specs and builds. (edit: There are also a couple of good Classic Warrior Discords. I’d recommend checking them out. There’s a Classic Community Discord list of links on classic dot wowhead)
Most people go with a deep Arms build, and can tank instances fine while leveling, but also solo some content for questing.
Spirit is great, if you are solo questing, and under ~30… it’ll help prevent downtime, and Warriors benefit from it more than any other class in the game.
Stormdragon brought up some great points, so I won’t bother reiterating, but here’s a low level Warrior Tanking Guide I put together.
You’ll notice there are some mixed feelings on two handed tanking, but I’d recommend taking some time to familiarize yourself with the full range of your toolkit, and add some weapon swap and stance dancing macros to your bars as well.