Use. The. MANUAL.
Also mark the thread resolved.
NOTE: If you don't know the function you're searching for, look for the topic it would be under in the manual. If you still can't find it, search using basic keywords. At the top of PHP's pages, there is a search box. Type in "create a folder" for example, change the dropdown box to "whole site", and click the arrow.
Oh look, search result #1: "Ideally mkdir should create the folder with the script's UID, ..."
#2: " over NFS is mkdir() which will either create a folder or return a error status. ... "
etc. ...