Explanation
In the example, the formula in cell D6 contains this formula:
=MONTH(B6)&YEAR(B6)=MONTH(C6)&YEAR(C6)
In this case, Excel extracts the month from the date in cell B6 as numbers, then concatenates them together to form a text string. The same thing is done with the date in cell C6, the month and year are extracted and joined together.
Finally, the formula then tests for equivalency using the equal sign. Both dates are in January 2000, so the formula is solved as follows and returns TRUE.
=MONTH(B6)&YEAR(B6)=MONTH(C6)&YEAR(C6)
=1&2000=1&2000
="1200"="1200"
=TRUE
If you need to test a date to see if has the same month and year as the current date (today), you can use this formula:
=MONTH(date)&YEAR(date)=MONTH(TODAY())&YEAR(TODAY())