How to leave only duplicates in EXEL?

Question

excel

Dear men!

Tell me, please, lady, how can I find duplicates in EXEL and leave only them? And delete everything else?
And how to prepare a table for such magic, if in the table on the right the cell includes two cells from the table on the left.

Answer 1

There are many options for finding duplicates. As one option, you can write the formula =countif(A:A;A5), where the result is greater than 1 will show duplicates.
For the second question, the formula =concatenate(A5; B5)

Answer 2

Answer to the first question .
Answer to the second question