This article is from the Amiga FAQ, by Ignaz Kellerer with numerous contributions by others.
No problem for owners of Workbench 2.1 or higher: The program CrossDos is part of the Workbench. All you have to do is mounting the device `pc0:' by putting it into the drawer `Devs:DOSDrivers' or by double-clicking the icon in `Sys:Storage/DOSDrivers'. Ms-Dos disks in drive `df0:' can now be handled in the usual manner replacing the word `df0:' by `pc0:'. For example the directory can be shown with the command dir pc0:.
People still running Workbench 2.0 or lower need a program called `MSH'. You will find this on the Aminet (directory misc/emu) and on Fish disk 382. See Sources. After editing the file `devs:MountList' as described in the documentation you have to say Mount msh: in the CLI and can now do the same as above replacing the word `pc0:' with `msh:'.