Hi Sharon. These are great questions.

For me it is very easy to notice these levels after decades of experience. For example when I am at beta state I feel agitation and my mind wonders.

In alpha level we gain much better attention and focus on a specifc duty. For example, entering flow state is used by millions of people.

Measuing other levels objectively requires technology tools. Learning meditation from books can be difficult.

I shared my meditation experience in this article. https://medium.com/illumination/why-i-meditate-every-eight-hours-for-decades-cfecd3e05ed1

This short video from an accomplished meditator might get you started. There are many great videos on YouTube. https://www.youtube.com/watch?v=Hzi3PDz1AWU

T