It's OK if this doesn't make sense yet; that's what the tutorial is for\. It's also OK if this interpretation raises more questions than it answers: Why are the logarithms above using base 10? What does it mean to say that a number is "two and a half digits long"? Why is it 316 \(rather than 500\) that is using two and a half digits?
Instead of telling me "It's OK if this doesn't make sense…" (No it's not okay! I was told this is a site where things make sense!) say a sentence that I find myself agreeing with, like:
"Wait, what do I mean that 139 is "close to" being a three digit number!? There are plainly three digits, '1', '3', '9', sitting right there on the page. For the answer, read on…"