this password question hasnt been asked

i am creating a site that needs password protection and loging with username
for a portion of it. I dont need iron clad security for this, but I do need
medium level securiy. I also need the user to be able to type in thier own
username abd generate thier own password in wich they can logon with. What is
the complete process of doing this...I am a begginer so I only know the basics
of dreamweaver. My webhostin gserver uses linix. Can anyone help or point me in
the direction of a complete tutorial etc that will get me from a-z?
Thanks ahead of time!