Furnace is a tool which allows you to create music using sound chips ("chiptune"), most from the 8/16-bit era.
it has a large selection of features and sound chips. from the NES, SNES and Genesis to ES5506, VIC-20 or even Arcade, Furnace has most likely covered your target with many presets to choose from.
every chip is emulated using many emulation cores, therefore the sound that Furnace produces is authentic to that of real hardware.
if you just want to jump right in and get going, we recommended you go through the quick start guide first. it should get you familiar enough with the program to comprehend the rest of the documentation.
Furnace uses hexadecimal (abbreviated as "hex") numbers frequently. see this guide for a crash course.
Furnace uses a music tracker interface. think of a table with music notes written on it. then that table scrolls up and plays the notes. for an introduction to a tracker interface, see tracker concepts and terms before using Furnace. there's also a glossary of common terms.
Furnace uses a flexible windowing system which you may move around and organize. see 2-interface and 3-pattern for more information.
once familiar with the tracker, look to 9-guides for useful techniques.
How to Learn Chiptune Trackers: video tutorial created by Button Masher. covers the basic mechanics of chiptune tracking using Furnace for demonstration.
Furnace Tutorials: video tutorials created by Spinning Square Waves. be noted that these may not apply to the current version.