I was also confused and frustrated by the lack of clear difference between the various database connection settings in Wappler on my first ~10 projects. It really took a while for me to understand.
Just one person's opinion, but I think database & deployment are the roughest areas to navigate in Wappler right now while learning, especially given the lack of organized documentation or updated guidance.
Here's a webinar from 2020 that explains some of the complexities that I think are causing confusion, if you want to dive into it... it is the only place I've heard/seen a lot of the DB Manager stuff explained, but like many docs about 1/2 of it is old info and that can be hard to parse.
I also understand just going with what works 
Good luck!