NationStates Jolt Archive

Hi, i am kinda new to Nation States and really dont understand much. I have been reading some Forun Topics and the one thing really troubling me is Militaries. Other threads have talked about people not being 'old enough' to by the units, what does this mean? Also, how do you know how much money your country has so you can purchase all this stuff and how do you know when it has been 'delivered'? Finally, where do you 'buy' it from, i ave visited the link to the Naval shop and understand that but i dont understand where to get the infantry, armoured units etc. Please help
Any information would be greatly welcomed, From me