The String of Bananas needs as much light as you can give it indoors; a medium to high exposure. If it’s in lower light, it won’t grow much if at all.
Just be sure to keep it out of hot, direct sun (especially in the summer months) & make sure it’s not touching any hot glass. Either way, it’ll burn.
If it’s not getting light from all sides, you’ll have to rotate it every 3-6 months so it does.
Watering? It’s hard to say exactly because so many factors play into this but every 2-3 weeks is good ballpark. You want to water your String of Bananas thoroughly & then let dry out before watering again.