Thanks for your service.
Advice:
BE VERY ATTENTIVE TO SAFETY. NO HORSEPLAY. THE ARMY AND YOUR DRILL INSTRUCTORS OR RANGE OFFICERS WILL CRUSH YOU IF YOU DON'T FOLLOW THEIR PRECISE INSTRUCTIONS.
Also, don't be the know it all or the 'gun guy.' Play dumb. Listen. Don't talk unless you're asked a question or told to talk. Don't sharpshoot others, meaning don't point out how others are wrong. Don't be a Blue Falcon (Buddy F'er).
As a fellow gun guy, however, you will likely come away feeling that you did not get to shoot as much as you wanted, and it was probably never much fun.
Finally, and pay very close attention here because I was an Army officer and JAG and prosecutor and defense attorney: The military is in a period of ZERO TOLERANCE for misconduct. Silly stuff you might do as a civilian is a CRIME in the military. Talking back to superiors. Crime. Missing work. Crime. You get the idea. The military is also downsizing. They are looking for ways to punish and kick out Soldiers. DO NOT hook up with other female Soldiers. It will the fastest way to get a sex assault or rape allegation against you. I've seen it happen, and it's common. Co-ed Soldiers partying, drinking, hook up... suddenly sex assault or rape allegations and men go to prison. Don't go out in Columbus (near Benning) and have a few drinks and try to drive. A DUI will land you in deep hot water, and end your career. It amazes me, looking back, at how many Soldiers ruined their lives through drugs, booze, or just really stupid decisions and were kicked out or went to prison. Okay, enough preaching. Back to guns.
I went through JAG Basic in Virginia (about 3 months in 2006) and Officer Basic at Benning in 2007, for about 3 months, then on to Airborne school at Benning (if you can get an Airborne slot, do it). Certainly our experiences will be different but this will give you and idea.
We spent a day or a few days learning about the M4/M16. Classroom, slideshows, theory. Aiming techniques. Breathing techniques. Max effective range. Capacity. Concept of ballistics. How bullets work. SAFETY. Lots of people will be learning and holding the weapon (or any weapon) for the first time. Lots of folks from liberal anti-gun states... some have no idea how guns work. MORE SAFETY. And yet MORE SAFETY.
Did the 'dime' dry fire tests. You lay prone, and your partner places a dime on the barrel and you gently squeeze the trigger without causing the dime to fall off.
The Army has multi-million dollar huge video game simulator video games, and have some at Benning. You will likely get exposure to these. It's like a small movie theater with a huge screen and various movies with interactive videos involving real actors who do different things. It's a really cool simulator, and you have to react to friendly people, people drawing weapons, etc. You have a 'laser tag' style M4 and have to shoot or decide to not shoot depending on the scenario. It's a excellent tool, and a low threat example of the dangers of modern warfare and counter insurgency (COIN) operations. The scenarios are very hard and excellent training.
Live range days suck. They really do. It's not like going to your favorite shooting hole. High stress. Lots of yelling. Confusing orders. Etc.
We piled on tons of gear, packed very tight into busses (if you have claustrophobia, prepare to be cured), and went to the range. Spent all day zeroing. Some people just could not zero. Other trips were qualification on the popup 300 meter ranges. You'll fire some combination of 10 rounds kneeling, 10 rounds prone supported, 20 rounds prone unsupported, or some combination thereof making 40 rounds. I forget. You can look online to determine the different levels of qualification for sharpshooter, marksman and expert. I forget the exact methods.
You'll also get assigned your Night Vision Goggles. DO NOT LOSE THEM. You'll get a infrared laser sight for your M4 and hit the range and do night fire.
As far as how hard qualification is, some has to do with your ability, and some has to do with luck. I qualified expert many times in the military with rifle and pistol. However, it's very difficult wearing body armor and a helmet when you're not accustomed to it. It can be quite difficult to get a good cheekweld or shoulder to stock fit with body armor. You might also draw an abused M4 that jams, or hit a target that doesn't go down because it's all shot up or faulty. Finally, it will be stress like most people have never experienced with several Noncommissioned Officers roaming around, shouting, bullying people, etc. So, don't get discouraged. Just do your best.
That's Basic Rifle Marksmanship, or BRM.
Advanced Rifle Marksmanship involves more dynamic shooting, lowering and raising your weapon, gaining muscle memory from safe to fire to safe with your thumb.
You will likely get MOUT (Military Operations Urban Training) with paintball simunition rounds in your M4s. Small unit tactics, clearing rooms, etc.
You will likely spend a lot of time in the field with blank adaptors and blank 5.56 rounds.
You will get sooo sick of cleaning your M4, getting it spotless for inspection.
Other weapons systems.
You might get some training on the M249 saw (5.56 belt fed), the M240B (.308 beltfed), or M2 (.50 belt fed), or the M203 or Mark 19 (grenade launchers that you'll likely fire paint ball rounds) on big open flat ranges with old vehicles as targets. You might also get some experience on the M9 on either a static or popup range. You'll get theory on hand grenades, and likely practice with dummy grenades.
I went into the military loving guns and camping. The Army crushes your interest in these things. Range day, and days in the field, were not much fun at all.
Good luck Soldier!