I'm taking the Memrise online German course. The format being what it is, grammar and punctuation are not addressed. Since you get to both hear and read the lessons, I've found myself focused on the use of apostrophes.
For example: komm, ich zeig' dir die Stadt! let me show you the city!
Why is there an apostrophe after "zeig?" Why isn't this "zeige?"
Also seen in: los geht's! let's go!; here we go!
I asked Google for examples and nothing I found explained the rules in a way that made sense. I even hauled out a textbook that I used ca. '79 that should have addressed the apostrophe and its usage, but it didn't. Not even the fairly useful "German for Dummies" had any tips.
Können Sie mir helfen?