Find Values in Column A and fill identical values in Column B

Hi

I am after some help on an excel sheet for which I hope someone can show me how to do it. So here goes.

In column A I have around 1000 unique cells, I need to find the same values for each in column B and then fill the cell. Column B will have multiples of the same value so each value will need to be filled.

I was going to start doing this manually but then realised it would take me forever so am hoping somebody can show me the way.

Look forward to an answer.