I am active duty. Might be going to Afghanistan soon.
I signed for 3 years. But I have a total obligation of 8 years inactive reserve, meaning if a MAJOR war were to break out, after I seperate from the Army, they can call me back and tell me that they need me. So no matter how many years you sign for you really signing for 8 in fine print. The day you sign on the dotted line is the day your 8 years start counting down.
I can tell you right now, 3 years would be your best option. Most MOS options are 3 years minimum(military police and other long training agenda MOS fields are 5 year contract minimum) You can enlist for 6 years... Not recommended though.
There is a 2 year option but it is 2 years of service AFTER you complete BASIC/AIT. And only a handful of jobs are available.
Going thru the ranks is complicated. Most recruits are E-1 (E-Fuzzy). Some are E-2 due to exceptional physical agility that they passed a PT before even leaving for basic (17-21 years old, 35 pushups, 47 situps in 2 minutes and a 2 mile run in under 16:36)
Also you can be promoted for ROTC, and referring other recruits to join. You will see the occasional E-3 or even E-4 in basic. They either have college under their belt or extensive ROTC. Usually E-4's are master degree holders and are completing basic just to turn around and go to OCS (officer canidate school) But in basic everyone is an E-1, dumb private... ****. I have been in for 8 months and I am still an E-1!!!! (i have a ****** battery)
But to get promoted in your duty station, score high on your physical training test, shoot well at the range, have correspondence course hours under your belt, have no article 15s (discipline), and be a high speed low drag soldier. E1-E4 are pretty much given to you after a certain point of being in long enough, anything after that e5-e9 is all done by boards and promotion points. Meaning you will NOT get promoted unless they have space to promote you and you DESERVE it.
I personally, went to goarmy.com and browsed thru all of the jobs. There are alot more than there are listed on the site. But you will get a general Idea.
The army has ALOT of jobs. Just browse for now. If you have anymore questions just drop a post.