First two terms you need to know:
Credit - How many hours you are paid for working (doesn't mean you are actually present, just that you "credit" X amount of hours for pay.

Block - How many hours you fly. Starts from door closing/parking brake reset and goes until door opens at the arrival gate. Note, block can be a lot more than actual flying if you have a delayed take off, a long taxi, etc.

Min guarantee is the minimum you will get paid monthly. Think of it as a "salary" type pay. If a company's min guarantee is 75 (they vary by company), then whether you work (credit) zero hours or 74.9 hours, you will get paid 75 X hourly rate.

So if your company schedules you to credit 73 hours in a month, you will get paid at least 75. However, let's say that due to ATC delays, flight delays, WX, whatever... you are actually present at work for more than those 73. Let's assume you actually WORKED 80 hours. Now you will get paid for 80 instead of 75.

And then there's over time, or premium pay. Let's say you only worked the 73 hours scheduled above by the company, but there was open time that you picked up at 150% (the company needed you to work more, and you volunteered to). Now if you credit 5 hours on those days you picked up, you will get 75 X hourly rate (for scheduled 73 hours), as well as 5 X 1.5 = 7.5 X hourly rate on top of your min guarantee.

Hope this helps it make more sense.