Coming from an HTML and CSS background, the php.ini file was a MYSTERY! After working with a bunch of live Drupal sites, I can say that these parts of php.ini are the ones I've had to deal with so far:

Adjusting the resource limit

I believe increasing the limit of these settings helps everything. For the memory_limit, make sure it's some high number like 96 or 128. You can look into the other two if you feel like your scripts are timing out. For some image-related modules with Drupal, you need to have a high PHP memory limit.

(By the way, those semi-colons ";" are used for comments)

max_execution_time = 300     ; Maximum execution time of each script, in seconds
max_input_time = 60	; Maximum amount of time each script may spend parsing request data
memory_limit = 18M      ; Maximum amount of memory a script may consume (8MB)

Dealing with File Uploads

This article from d.o (how cool people say "drupal.org") helped me to understand how file uploads related to my php.ini file.

There are two settings to change so you can start uploading bigger files to your website:

upload_max_filesize = 2M
post_max_size = 8M

That article says the post size should be bigger than your upload size. My upload is set to 10 and post set to 20.