I want to build a web app for myself that will allow me to post stuff to Craigslist and retrieve postings from Craigslists. I am not doing this to spam Craigslist, I am just doing it to learn.
My question is: Is this possible? If so, will knowing PHP be enough? Or will I also need to know how to use the cURL library?
I'm pretty sure Craigslist looks down on scrapers.
You will need to use cURL, or file_get_contents() if your host allows it.
cURL will be easier however, as you won't have to deal with context for POST stuff.
If you just want to learn and don't want to get into trouble (legal or ethical), scrape a site where you have permission of the site's owner. Or even easier, make your own site and then scrape it yourself (via HTTP).