Fight practices are essentially a combination of the "New Player Talk" that happens before each game and an extended combat training for both new and more experienced players. We go over basic game mechanics including combat, magic, armor/body points, healing/dieing, etc. with the new players first.
The reason these practices are called fight practices is that many players (especially those who already know the basic mechanics) use them to try out various combat styles and get more technical practice with the weapons and combat techniques (which may be limited by the available weapon physreps). This is why fight practices can help players of all skill levels and are not only for new players.
After the rules training and fight practicing, a few in-game practice modules or "mods" are run, which is when the in-game practicing actually happens. The greatest benefit of the fight practice in-game mods is that you have a longer time to put those theoretical rules into practice without any risk to your in-game character, as things that happen in fight practices do not affect the actual campaign plot, items, or anything else related to the "official" game. Also, it's a great time for character concept experimentation, such as a player who normally plays as fighter trying the game as a scholar.
Andrea, if you want to coordinate one soon-ish (sometime in December), let me know. If there is enough player interest for one, I'll volunteer to run it (although I am not able to host).