Apple has made it way harder to set up a web dev stack in Mavericks than what it needs to be. The guides I've looked at are all pretty lacking in one way or another. If you're just trying to run apache for something quick/simple then press on. If you plan on doing anything remotely more intense such as scripting or long term dev, look into another easier to use stack like xampp. You'll save yourself some hours of frustration.
The issue you're seeing is a permissions related one. Theres a number of things that could be wrong here, but off the top of my head...
1.) The file you're trying to read doesn't have proper permissions. Go into terminal and make sure its chmod 644 for a static file or chmod 755 for a script.
2.) the directory or one of the parent directories your content is in doesn't have proper permissions. Say your apache conf is set to use /foo/bar/mywebsite/. All 3 of those directories 'foo', 'bar', and 'mywebsite' need to be chmod 755.
3.) you might need to play with chown'ing /foo/bar/mywebsite to _www or your username.