“The cello has no frets! How do you know where to put your fingers?”
Finger placement uses multiple senses. Primarily I use my ears to place my hands on the fingerboard. However there is a kinesthetic aspect to playing. I remember what a note feels like and what the distance between notes feels like. So I use touch to acclimate myself on different pitches. Additionally as I move closer to the bridge, I will occasionally check in with my eyes to see if the finger is in the right place. However, trying to look at my hand when it is closer to the scroll, is not helpful. It skews all the notes because the physical approach to the cello changes.
Using a combination of hearing, feeling, and seeing, and a memory reference of the note, I can know where to put my fingers. It truly is easier to do than it is to describe!