So slightly more focus on why they're different and how.

A bachelor's degree to a certain extent is generic. Generally you're going to take a lot of classes not directly related to your degree like English, math, history, art, foreign languages etc. My undergraduate degree was a bachelor of science in Economics and I took classes on theater, pottery, environmental science, criminalistics etc. that were all required for my degree (or rather they required I take X number of classes in different areas like physical science and art). Some requirements are specific, so I was required to take statistics which is related but I also had to take any 2 additional math classes and took calculus 1 and 2 which were not required for my degree. Then I also had to take X number of economic classes. Sometimes people do 2 bachelor's degrees but if you're luck there will be a lot of overlap between the 2 requirements and you'll only need to take the specific classes related to the 2nd bachelor. The goal was to establish a broad base education.

Then once you have a bachelors you can go and get a Master's in a specific field and you'll generally only need to take specific classes related to that field. My masters is a Masters of Accountancy, for 2 years I only took classes that were directly related to accounting; audit, taxes, forensic accounting, and accounting ethics. The goal was gain a higher level of understanding in a specific subject.

If I ever went back and did my PhD then the focus would be on research, modeling, tools, etc and a lot of those classes are more about how to perform and document research over all than related to the PhD field you're in. Then you perform your research and write a doctoral thesis dissertation where you'll try to expand on the knowledge of the field as a whole and you may have to defend your research against a board of other doctors in that field.

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So you're going to start with an undergraduate degree then if you want a 2nd degree you can decide if you want a 2nd undergraduate or a masters. Once you have a masters you can decide if you want a 2nd masters or a PhD. It's just a matter of how deep you want to focus.