2008 MacBooks typically have at least Mac OS X 10.5. They can at least be updated to Mac OS X 10.7.5. Late 2008 MacBooks can go up to 10.8.4, but early to mid 2008 MacBooks only can go as far as 10.7.5. But before you go that far, you need to determine if you have any Mac software from pre-2006. If you do, you won't be able to upgrade past 10.6.8 without updating that software and its documents first. Appleworks is a classic example of that problem.
So first look at the 10.6 system requirements, and see if you are ready for it. Next go to Apple menu -> About this Mac -> More info or System Information, and look at the serial number. The 3rd, 4th, and 5th character are the key characters for determining the age of the machine. xx843 to xx852 where x can be any letter or number are the only ones that can upgrade to 10.8 or later. W8843 or 5J843 are the same age. Do not tell us your serial number. Then if you find you your hardware is 10.8 compatible, consider upgrading to 10.6.8 first and then purchasing 10.8., and then downloading 10.8.4 if your software is also compatible. If you find you are only 10.7 compatible, you only need to get the 10.6.6 combo update before upgrading to 10.7 and then 10.7.5.