I believe your bike has a double crankset with 50-34 chainrings.
The general advice is to attempt to avoid cross-chaining, i.e. avoid the big ring and biggest 2-3 cogs in the rear, and avoid the small ring and smallest 2-3 cogs in the rear. There is actually some empirical testing that shows that these combinations create higher friction in the drivetrain, and they likely wear the chain and cassette out faster also.
I'm pretty sure that with almost all groupsets, you can expect the chain to actually shift to all the cogs. In the small ring and smallest 2 cogs, the chain rubs against the front derailer cage quite noisily, but the rear derailer does actually make the shift. In my experience, big ring and biggest two cogs are slightly noisier, and you can often trim the front derailer to reduce the noise (that is, the left shifter often can actuate a partial shift which moves the cage slightly, but not enough to go to the small chainring).
Practically speaking, it is fine to leave the chain on the big ring most of the time, and to shift to the small cog when climbing significant hills. I find that at most normal solo riding speeds, a 50t chainring leaves me in the middle cogs on the cassette. Thus, one rubric I use is that if I hear the chain rubbing the front derailer slightly, I'll downshift in the front (i.e. shift to small chainring, which decreases the gear ratio) and simultaneously upshift in the rear (i.e. shift to smaller cogs, which increases the gear ratio). With the small rings on modern setups (i.e. 34t or 36t), many riders will probably be in the smaller rear cogs on flat terrain, which is not optimal for reasons discussed above.
In the past, when typical gearing was 53/39 and cassettes had tighter ranges (e.g. 12-25 or 12-23 in the rear), riders may have been advised to leave the chain on the small ring most of the time. I certainly recall being advised to do this by people in my cycling club. I believe it was conventional wisdom that you wanted to learn to spin the cranks smoothly, at a relatively high cadence. I don't know that there was a lot of empirical basis behind this advice, i.e. it could just have been fashion. Most newer cyclists will pedal at relatively low cadence, and will probably work their way up to a more optimal cadence gradually.
NB: please read what Adam and Argenti said about overlapping gear ratios between your two chainrings.