Some authors prefer to place their manuscript LaTeX source files in a subfolder, and other research artefacts (figures, tables, etc) in another subfolder. This example shows how this workflow can be maintained on Overleaf, by providing a top-level main.tex that pulls in the real main LaTeX file from the subfolder using the import package.
Some examples of how the packages tikz and pgfplots can be used to create fully vectorized graphics directly in the LaTeX document. An example of how a flowchart can be generated in LaTeX is also given. It combines the packages tikz and overpic and shows how to overlay/embed intrinsic LaTeX text onto images created elsewhere.