A lot of these could almost be categorized as notes to myself to better remember why I added them. For example, Front Line Offensive 1915 is likely added to just give the AI a bit of an extra push via a few extra units for a planned offensive at that time.
Most are just as they say, e.g. drop a Corps at that location for that date and so on.
Quite a few are also conditional, but this is not in the description and you'd have to take a look at the script itself.
For example, some might have this in the event which just means it will only fire if the CP has 1 unit, within 2 hex range of 155,84 and so on.
; Central Powers units in range in 155,84
#CONDITION_POSITION= 155,84 [2,2] [1,1]  
The idea was to not just put a bunch of extra AI units in there and call it a better AI, it is very fine tuned to the various levels and threats or challenges the AI will receive during the course of the war.
For example, a lot of those conditional events will never fire if the AI is doing well (e.g. the defensive bonuses) or if it is doing poorly (e.g. the offensive bonuses) and so on.
The UNIT event itself can be found in the campaign subfolder (in the root installation folder) for the particular campaign under the 'Events' folder.
Hope this helps,