Lets use some nice, easy, round numbers to illustrate these concepts.

APR is short for Annual Percentage Rate, which is the interest rate that is credited to the account. For our example, let's use 12%. Let's use a nice, round starting balance of $10,000 for our deposit.

Charging interest more frequently than once a year means the annual rate gets divided and applied based on the frequency. So if you have a 12% APR and interest is applied annually, at the end of the year, you will be paid $1,200 in interest. If you have a 12% APR and interest is applied quarterly, then at the first three months, you will be paid $300 in interest. (12% / 4 = 3%) If your interest is applied monthly, then at the end of the first month, you'll be paid $100 interest (12% / 12 = 1%)

Compounding interest is when the interest you've earned gets added to the deposit balance that's eligible to earn interest, and this is where the frequency of interest being applied starts to matter.

Let's say you earn interest twice a year. At month six, you will earn $600 interest. (10,000 balance, 12% APR, twice a year means 12/2 = 6%) At month twelve, you will earn $636 interest ($600 interest from your original $10,000 deposit, plus $36 interest on the $600 interest you earned at month 6!)

So at the end of this year, you will have earned $1,236 in interest on your $10,000 deposit with a 12% APR. The annual percentage yield (APY) on your investment would 12.36%. If your interest was applied monthly, your APY would be 12.68%. More frequent compounding leads to a slightly higher APY with the same APR.

>Is your credit score looked at at all when opening one? Does having a better score mean you get a better rate on investment?

Nope, and nope. The rate is based on the amount you deposit, and in some cases, there may be additional restrictions on when or how much you can withdraw and keep the same rate.