[sriku]

This is good advice.

I'd add that producing something as part of your process of understanding the code base would be helpful to your colleagues.

If there is hard to understand code, figure it out and capture it in some documentation. If some code doesn't look robust, add tests. If you find bugs, log them and write tests. That way, your colleagues also understand the process you're taking during your "grok the code" period, see progress and can jump in to help. Having a top level understanding of the system and its business functions is important so you can evaluate code your read relative to them.

Adding type annotations can be useful, so try FB's "flow" which gives useful results without having to do any annotations yourself for starters.