4DOS
DSx86 does not have an inbuilt command interpreter (or shell), so you need to also download a DOS program that provides the command shell features. Currently the only supported shell is 4DOS version 7.50, freeware by Rex Conn & JP Software. The only file you absolutely need is the 4DOS.COM program, but if you have space on your SD card you can download the auxiliary files as well.
The recommended place to put these files on your SD card is /data/dsx86/4dos/ directory, but also /data/dsx86/, /4dos/ and root directory will work.