There are a few ways to use Langchain. Firstly, the docs are a mess. What I personally did, I followed the notebook from OpenAI cookbook on embedding a code base, and one on embedding the docs, and querying over that with GPT-4.
After a while of doing that, I realised like many others that it's too high of an abstraction. In the end I think you're better off just looking at their source code, and just looking at how they've implemented the stuff in normal python and then adapting it for your own needs.