How do you find undervalued stocks for long-term value investing?

Hey everyone!

I've been reading a lot about Warren Buffett and value investing lately, and I'm really interested in finding good companies trading below their true value. The problem is, I'm not sure where to start or what to actually look for.

I understand the basic idea of buying stocks that are "on sale," but how do you actually find these opportunities? I've been looking at P/E ratios and trying to compare them within industries, but I feel like I'm missing something important.

Right now, I mainly just invest in index funds, but I'd like to start building a small portfolio of individual stocks for the long term (like 10+ years). Any tips on what metrics to focus on or how to screen for potentially undervalued companies?