I can certainly understand if you feel a bit intimidated. Last time I counted was a few versions ago (3.0.1)
Total number of PHP files searched: 269
Total number of PHP files with Classes or Functions found: 167
Total number of PHP classes found: 168
Total number of PHP functions found: 3856 - [ver. 3.0.1 - 3859 functions]
That's a lot and that doesn't include any found in plugin or theme files!
Though idle perusing might spark some ideas, as jaagare said, better to get to know them on a "need to know" basis.