How to parse a 3d model from a file?

Question

C++ / C#

There is a file, you need to parse the model according to the structures. Where to begin?

Answer 1

Start by examining the file format in which this model is represented.

Answer 2

You need to start by defining the structure of the data stored in the file and determining the storage format of the model.
Until this is done, there will be no further progress.