If you're using English excel then you would need to change the commas in the formula to semicolons.
To help you understand it, MONTH(TODAY()) returns the current month in numeric form, Jan =1, Feb =2, etc.
The logical test, <7 checks to see if the date is in the first 6 months of the year. If it is, the formula returns "B" if not it returns "C".
The next part is a little more complex, again it takes the current month number, but then it changes it. If the month is < 7 then it adds 1 (so Jan becomes 2, Feb 3, etc). If it is 7 or more then it subtracts 5 (Jul becomes 2, Aug 3, etc).
By joining the resulting number of the second part to the letter from the first part you get the location of the month in the table.
Using today (August 26th), the month is not < 7 so the result of the first part is "C" and the result of the second part is (8-5 = 3). Join them together and you have "C3" which INDIRECT converts to a valid cell location on the sheet and returns "aout" from C3.