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 3.0 through 98(SE) can be installed inside DOSBox however this is unsupported and instability issues occur. At least one person has gotten Windows ME to work.
You could also, alternatively, install FreeDOS (or just it's included utilities) for a more complete DOS experience.
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.
DOS/32A is a more advanced extender and open source replacement to DOS4GW. It can improve both performance and stability of many games. More info here.
Although DOSBox will not gain the performance improvements this program promises, it will add additional video modes. Although 5.0+ were initially released as commercial software, SciTech later released them as freeware. Versions 1-4 were always freeware though. The 5.x series is generally the best to use with DOSBox. Additional (possibly useful) DOS display utilities can be found here.
The Gravis Ultra Sound or GUS was a sound card produced by Advanced Gravis Computer Technology, who were best known for their Gravis PC Gamepad. One of the features of the GUS is its ability to use real world sound samples instead of digitally generated instruments. This allows for a richer quality of sound when playing midi sound. Unfortunately, the official patches (drivers/samples) cannot be distributed with DOSBox due to conflicting Licenses. You can however find some here.
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.