This is a shelf made for Zerup bottles, as produced by More Nutrition. These shelfs are designed to be applied on a flat surface with double sided mounting tape.
There are multiple variants of the shelf, with 2 to 8 slots for bottles.
Mounting the shelfs in multiple layers, can easily be done with the included mounting tool. This tool is used to ensure correct spacing between the individual shelfs, allowing for easy access to the bottles. To use the mounting tool, print the file two times, to have two brackets.
All variants are provided as STL and STEP files. The most commonly used format in 3D printing is the widely supported STL file. STEP is an alternative format, primarily meant for engineering. The advantage of STEP over STL is, that curves are actually expressed as curves instead of many triangles. This will allow your slicer to produce smoother curves. But this requires that your slicer is actually capable of slicing STEP files.
BambuLab Studio actually supports STEP files (more details can be found on the Wiki: https://wiki.bambulab.com/en/software/bambu-studio/step).
If you're unsure which file you should use or which capabilities your Slicer software has, use the STL.