[sqs]

First, get your tooling set up, especially a code search tool with go-to-definition and find references. A good code search tool will make you much faster and better at understanding code, finding correct usages, debugging problems, etc.

It also makes it easy to get a URL to any line/region in a code file to paste into email/Slack to ask/answer questions. (Of course, GitHub has URLs, too, but you probably aren't browsing code on GitHub already because it lacks code navigation/intelligence features, so getting the GitHub URL would add an extra clunky step.)

Here is a study of Google's internal code search tool with some example use cases and interesting stats: https://research.google.com/pubs/archive/43835.pdf. Most(?) engineers at companies with large codebases use code search frequently if they've ever tried a good code search tool (i.e., it's hard to give it up once you've used it).

(Disclaimer: I work on a tool that does this, but I'm omitting the name/URL because the advice is general.)