For someone new to cycling you're doing well with the terminology!
The simple answer is that you only have two chainrings, so there's no "middle". With luck there will be a wee display on the top of the shifter, but that's not always present. And with only two, eventually you'll just remember which you're in (link is to a "how do I know" question).
If you're asking about gear selection, it isn't really about "uphill gears", "middle gears" and "downhill gears", it's about what's comfortable for you. Different people are more comfortable at different pedalling speeds, and as you cycle more you're likely to find that that changes. So the "middle gears" are the gears you feel comfortable in at your "middle speed" :) It's hard to expand on this because it really is as simple as "whatever works for you".
For now, I suggest not worrying about which chainring you're on so much, just focus on getting comfortable changing gears. The next step is trying to avoid cross-chaining (the big chainring with big cogs at the back, or small-small). This question has some tips on that, and this one has a different view. After that people tend to worry less about which gear to be in and more about optimal cadence, muscle efficiency, how fast bike parts wear out and other stuff like that.