Natural log, Common Log, and Euler's Constant

There are only a few things lo learn today, then everything else is old news.

If a log doesn't have a base written, it's base 10. That's the "common log".
There is a number related to natural mathematical occurrences called Euler's Constant. We use e to denote it. It's kind of like pi. e=2.718....
A log with base e is called the "natural log". We don't use the write "log" for that, we write "ln". There is an LN button on your calculator.

Everything else is using what we already know about logs along with this.