The credit limit on a credit card is the total they will let you borrow on it, ever. You can spend it all in the first week if you want to, but then you can't use the card again until you have cleared some of the balance. (Going over the limit on your credit card is horrendously expensive and wrecks any special balance transfer or special offer rates you might be on, btw.)
No- they are ongoing and apply at all times. Boxtops' answer probably covers it. If not, GWK, please can you clarify what exactly is it you need to know.