apropos(1) just seaches a large text file called whatis. Each line in whatis contains the name, section number and short descrition of one man page in your installation. whatis is created by a script called /usr/sbin/makewhatis1?.
If you find that apropos(1) never finds anything there may be be no whatis file yet. Run /usr/sbin/makewhatis as root (see su(1)) and it will be created. (Note: /usr/sbin/makewhatis can sometimes take several minutes to finish.)
Section (3) man pages contain descriptions of C and TCL library functions for programmers. There are so many of these that they overwhelm everything else. You can remove them from whatis. As root, edit the script /usr/sbin/makewhatis. Around line 75 you will see a line like this,
sections="1 2 3 4 5 6 7 8 9 n l"
Remove the "3". Run /usr/sbin/makewhatis again, and the section (3) entries will be gone.
One page links to MakeWhatIs:
lib/main.php:944: Notice: PageInfo: Cannot find action page