Common elements in an column in a given dataframe using pandas

In Assignment three there were multiple instances where we had to find the common elements of two given data frames in python.
Like in this :


and this data frame:

*We have to find the common countries in those data frames
Are there any specialized methods to do this operation? As I found pd.merge() online but didn’t quiet understand its usage.
*We have to find the common countries in those data frames