DOSBox does not use a graphical user interface. However, front ends such as D-Fend Reloaded (an updated successor to the program D-Fend) can be used.
There are various unofficial builds of DOSBox which provide additional functionality such as support for Glide. A full list can be found on the DOSBox Wiki.
For Windows and Linux, a good one to start with is DOSBox SVN Daum. It streamlines the interface and adds support for features vanilla DOSBox cannot do such as Glide support. It is used in some of GOG.com's DOS game releases.
It can be downloaded from the Official Site.
For Mac, you should try Boxer. It makes running and installation of games easier by wrapping them in Application Bundles, called "Game Boxes", that can be launched in Boxer by double clicking them as well as having a builtin GUI interface for configuration that more easily integrates into the Mac OS. It also has much over looked audio features; it already includes Gravis UltraSound patches and has builtin CM-32 & MT-32L emulation available through MUNT.
Windows 95 and Windows 98 can be installed inside DOSBox however this is unsupported and instability issues occur.
DOSBox running in Windows:
Z:\>mount c c:\game_directory
Z:\>imgmount d d:\game_disc.iso -t iso
Substitute the pathways with the given conventions of the host operating system.
Alt+↵ Enter to maximise the window; Ctrl+F4 to switch between mounted disc images. Use double quotes, " ", when mounting folders with spaces ("c:\installation folder"); For mounting multiple disc images, -t iso is required only once at the end of the last disc image, this defines how DOSBox should emulate the volume and iso defines the type of volume.
DOSBox stores configuration information in *.conf files. Individual conf files can be create for each piece of software used and additional parameters can be appended.
To modify a configuration option within DOSBox, use the config command. For example, config cpu cycles fixed 30000
config cpu cycles fixed 30000
The DOSBox Mapper (Ctrl+F1/⌘ Command+F1) can be used to reassign keyboard, mouse and joystick commands.
DOSBox has several virtual joystick modes which affect what inputs are seen in-game and also what inputs can be remapped using the Mapper. See the DOSBox manual for details.
Some games have fixed inputs. Use the DOSBox Mapper to remap the controls.