First, you will want to read the links that Erik posted for you in his message. I also recommend that you read the complete tutorial linked to right over there (<---) on the left side column.

As for "configuring" individual pins as input or output, it's kind of misleading to state it that way. When you say that a port is "configured" as input, it simply means that you've written a 1 to that pin. It will then remain in the high state as long as nothing external pulls it low. And of course anything you write can be read as output.

The tutorial on the left and the links that Erik posted will explain a great deal about how to use pull up resistors if necessary and you can also find many threads in this forum discussing the subject at length.

Good luck.