Here are a few places to start:
First from the UK
Understanding Digital Camera Histograms: Tones and Contrast Understanding Digital Camera Histograms: Luminosity and Color
From the US:
https://luminous-landscape.com/understanding-histograms
From Australia
Understanding Histograms - Digital Photography School How to Read and Use Histograms - Digital Photography School
From somewhere:
https://photographylife.com/understanding-histograms-in-photography Digital Photography Tutorial: Histogram - Photoxels
and on and on and on. Bingle is your friend here. Type in digital photography histograms and you will get millions of hits off of your favorite search engine.
In essence a histogram displays how your cameras JPEG engine detects the spread of light across the exposure. The thing you look for is "clipping" where the values displayed are packed up along either the far right, the far left or both. In an ideal world the histogram would show an even distribution of values - but shooting grey cards gets really boring after a while
The real world has loads of variation and the histogram is but one tool to assist in its control. And for heavens sake shoot RAW - the more data you have to work with, the greater control you have over the end product.
The Elitist - formerly known as PDL