Hi Toastmaster,

Welcome.

Dazzle's link points to a site with info on the Kagyu school. It doesn't give information on other sects or schools. For info on different schools and sects, you can try the following:
link -> Buddhanet
link -> Wikipedia article on Buddhism

There are other sites with information, but these are good places to start.

This is not a good book. I read three chapters at different places in the book and found all three full of errors. The author claims scholarly support for statements that few scholars would support, and doesn't seem to be aware of the Buddhist scholarship of recent decades. Fifty years ago, this book might have passed muster, but it's not something I would bother reading now.

Examples of problems:

The author claims that meditative practices of late Vedic India (the time of the Buddha) were derived from the much earlier Indus Valley civilization. While there is evidence of cultural continuity in the areas where the Indus Valley civilization flourished, that doesn't support the claim that late Vedic religion was derived from Indus Valley religion. Since we know almost nothing about Indus Valley religion, it's not possible to support claims about this.

The author writes that "the written canons of the Theravada and Mahayana traditions date to roughly the same period." The Theravada canon was written down in the first century BCE. The Mahayana sutras date from the first century BCE to 1,000 CE. For example, only the two earliest Mahaprajnaparamita sutras were written betwee 100 BCE and 100 CE. The remainder were written between 100 CE and 1,000 CE.

The author conflates the "Mind Only" school with the Yogachara. Recent scholarship makes clear that "Mind Only" was a later development within Yogachara, and doesn't represent all of Yogachara. The author's description of "Mind Only" is an inaccurate description of Yogachara.

Those are just three problems out of many that I saw.

I'm aware of Santina's resume. Unfortunately, it doesn't make up for the deficiencies of his book.

The original poster asked for a description of the various sects of Buddhism. This book doesn't do that. It presents the traditional Tibetan view of Buddhism. Theravadins make up one third of Buddhists world wide, but this book mentions Theravada Buddhism only in passing, as background to Tibetan Buddhism. Pure Land Buddhists are the largest group of Mahayana Buddhists, but this book doesn't mention Pure Land at all, and Amitabha Buddha is mentioned only in the context of his role in Tibetan Buddhism. While the subtitle is "An Introduction to the Major Traditions of Buddhism", it's actually covers only traditions within Tibetan Buddhism.