extenal hard drives

Hi everybody.

I have recently moved from a Windows 7 64 bit PC to an imac.

I have several external hard drives which I want to use with my imac.

What do I need to do to make them accessible on the imac?

I need to keep the files on the disks, but I still have my Windows PC in case the files need to be moved off the
disks for formatting purposes if necessary (hopefully not!).

Any advice very gratefully received

Many thanks and kind wishes

Jim