Where do I put stuff in a growing codebase?

I've mostly been putting functions, structs enums and tests in the same file and it's starting to feel like a mess... I am constantly losing track of which function is where and I'm never quite sure if I have code in the right place. I know this is kind of vague, but that's been my general feeling while working in my largest personal project so far. It's essentially a large Algorithm that has many smaller steps that needs to run in a sequence.

I think I might just have too many loose functions and maybe I should use more impl methods and traits? I'm also thinking I should try the builder pattern in a few spots.

Anyone have any guidance on code organization in rust?