Now I am assuming that you are on a pc, wanting to transfer files to the amiga.
If you have Workbench 2.1 and above you will have the ability to read pc-disks right out of the box. Just mount PC0: which per default is located in the Storage/Dosdrivers/ directory. One thing to remember though is that you will probably have to use a DD-disk (720KB) as most amigas doesnt have HD-diskdrives.
If you dont have Workbench 2.1 or above you can use
MSH to read ms-dos disks, though this presents a moment 22 case as you cant transfer this program to the Amiga via disk from the pc without being able to read ms-dos disks.
If this is the case, you could transfer files via a nullmodemcable if you have any sort of terminal software on the Amiga.
When you have the file on your amiga, you can use
DMS to unpack it onto a disk.
/Patrik