Credit Card Question: Complete Noob

I am completely new to credit cards and am wanting to get one.
I have no kind of history, and i am a student, so i plan to get one of these.
I will use the capitol one standard platinum as an example.
Ok, so first off, the capital one standard platinum credit card has a limit of $300–$3,000.
does this mean i have to spend between 300 and 3000 dollars in my purchases?
or does it mean that the limit can vary from 300 to 3000?
and i understand now that the interest charged will be monthly?
like lets just say i have 18.5% or whatever, and i buy a 100 dollar item, i will have to pay 18.50 dollars after the first month and 18.5 percent of my balance after the second month and so on?
if that's sooooo, then why do they call it an ANNUAL percentage rate?
I have more questions, but i've noticed they don't all get answered when i ask too many, so i'll ask after these get answered.
thank you. please help, i've been trying to find info everywhere.

[Jeanie]

Gerardo,

The $300-3000 limit is the limit you could get from the credit card company (that may increase in time) which means if for example you get $400 limit from them, anytime you exceed over $400 ($400.01+) you will be charged a fee (whatever the fee is they state in their terms). For the APR (annual percentage rate) is a a percent of whatever your balance is monthly. Yes, this can go up, so it is always best to pay your FULL balance to void all APR fees..

Hope this helped..

~Jeanie