Working locally with MAMP is awesome, but what about when you need to take that site live? Last time we got a version of WordPress installed locally, now we'll take that local version and move it to a real live site. This entails moving files as well as moving the database, and changing a couple of values in that database.
Links from Video:
Regarding the user setting in MAMP, Luke writes in:
If you're connected to the internet, and someone is able to find your External IP address, suffixed with :8888, they will be able to access your local web server (may or may not be desirable). However If they decide to do some unethical stuff (e.g. exploit your site) they can do some pretty nasty stuff.
If you don't change your user in the MAMP dialog to www/MYSQL then they could potentially access your data outside of the local web dev section, delete your data, etc. Basically they will have the same permissions as the user that's running the MAMP server. So if you're running it as root, or your local user, they can potentially delete your data, view your data, edit your data, etc. However the www/MYSQL user by default only has access to read (no write) the data within your local web dev area and nowhere else.
To get around permission errors, on a Mac, you would just have to change the permissions. Go to the file/folder you're trying to access, right click and View Info. at the bottom there is a box for permissions, and just change for the user _www (add it if it's not in the list, it might be www) and give it read and write permissions for whatever it needs.