Hello fellow devs, hope you rocking! I need your advice as junior dev here. How do you handle big projects ? I mean, without getting lost when coding and having a clear understanding of code's flow.

Everyone gets lost and none has clear understanding of the flow

Honestly? Practice.

(Games like Factorio and TIS-100 can also help if you're struggling)

Understanding how a large project works in its entirety comes down to working with it overtime.

No one knows everything, unless you have written every line code and have a decent memory.

Database visual relationship schemas(MySQL Workbench is decent as a free software) and functionality/action-flows graphs(yEd).

On the software side, layers for separation of concern (Business-Logic-Layer (BLL)|Data-Access-Layer(DAL))