Are your addresses in A1, A2,... or A1, B1, C1,...?
Assuming they are in Col A
enter this in B1
=A1
and this in B2
=B1 & "," A2 and copy down till end of your data
In the last cell of Col B you will get your addresses separated by comma
If you have data in Row 1
then in A2 enter
=A1
in B2 enter
=B1 & "," & A2 and copy right...