Got my first credit card, I'm kinda lost?

you have a limit of 500.00-a credit card is essentially a loan, you use (borrow) 100.00 then your available balance is 400.00. it is best to pay it off in full each month so your available balance goes back to 500.00. These are all questions you should have asked BEFORE you got the card.

They don't refill it completely until you pay off the entire balance in full.

Each month, they refill it by however much you paid, but they also take out fees and finance charges. So, for example, if you have a $500 limit and spend $100 and pay $30 and the fees and finance charges are $10, then the amount available would be $500-$100+$30-$10=$420. If you then wanted it back to $500, you'd have to pay another $80.

Your best method for improving your score is to pay off the ENTIRE BILL each month ON TIME. Every time you pay off the entire bill your credit available balance goes back to $500

That's not how you boost your credit. You use the card and pay it off every month. Owing and not paying it off simply says you can't manage even a small debt.

When you hit the $500, you won't be able to borrow any more until you pay it down. If you pay it off regularly, they will increase it without you asking.

The best way to improve your credit rating is to have ONE card. Use it and pay it off every month. Do NOT spend more than you can pay back (unless you have a true emergency, like a car breakdown or medical bills.) I've raised my score over 200 points with just one card used wisely.

Yes. PAY IN FULL every billing statement. #4 Then you have the right to borrow (via using the card) the $500 the next month (but I suggest you stay below $200 each month). Do not WASTE your money, but buy things you need. There is no refilling. (see #4). It takes 1 - 2 years of proper use for a credit score to go up significantly.