The "2 cell" generally means how many cells in series. A 2 cell lipo (7.4 volts) may have 2 actual cells or it may have more
The full description would be 2s1p for example - 2 cells in series, 1 parallel, the difference is how they are wired. Cells in series add voltage while cells in parallel add their mAh (capacity) but not voltage. It's usually just said as "2 cell lipo" because the voltage is what really matters in terms of equipment compatibility.
You could have several ways to make a 7.4 volt 5000 mAh battery pack. At 2s1p it would be two cells in series, each cell being 3.7 volts and 5000 mAh. Or it could be 2s2p which would be four cells total, each cell being 3.7 volts and 2500 mAh. Two pairs are wired in parallel and then those pairs are wired in series. In actual use there is no difference between those two packs, although the size/shape could be different.
The "C" rating is the discharge rating, 1c equals the total amperage capacity of the battery. So a 20c 5000 mAh pack is rated to discharge 100 amps, while a 40c 5000 mAh battery can deliver up to 200 amps. The thing to remember here is that C ratings are highly subjective. Usually that rating is to indicate the "continious" discharge - meaning the battery should be able to deliver that many amps over a period of 10 seconds or more continiously. However it could also mean the burst rating (up to 3 seconds only), and you also have the confusion that there is no real standard for measuring discharge ratings. Some companies will over rate their batteries while some will under rate them. Confusing yes, but in general you can use the C rating to determine the quality of the cell.
That also means that, assuming the ratings are accurate and using the same method, a 40c 2500 mAh battery can deliver the same amperage as a 20c 5000 mAh battery - 100 amps in both cases. The 5000 mAh battery could do so for longer as it has more overall capacity however.