You can do this using forms and the database wizard.
You have to make a form (Insert Menu > Forms) and put all the form elements
on the page, give them field names. etc.
Then set up the database results wizard to make a database connection based
on the form field names - it will be an *.mdb file (MS access format).
Regarding Username, Password functions this is a little more complex but I
believe it can be achieve by setting permissions on sub-webs. Check with
your host about if they allow this. (I've never done it this way - have
always used third party scripts)
For the above to work your server must be running the server extensions,
else you need to look for thirdparty products to do all the above, depends
also on what scripts your server supports (PHP, Perl/CGI, ASP, Sharepoint,
ASP .Net etc).
There are password scripts and user-management type applications around, you
just need to start making a search around the web for them.
A good starting place is
www.hotscripts.com for scripts to write to a
database but what you require depends on the level of security you want etc.
I am currently using
www.locked-area.com - a set of Perl scripts for
Unix/Linux server - nothing spectacular, but it is a user-management system
that people can sign up, and become "members" of the site. It uses the
htpassword and htaccess methods in the Unix/Linux systems, and can be
integrated into your existing web site design.
Another site I'd really recommend for you if you're using a LInux/Unix
server is
www.ezscripting.co.uk - flatflile database, perl scripts. This is
for simple applications and not the most secure of databases in the world,
but it does the job for non-essential security type applications. Results
pages for searches etc can be integrated into your current design - they use
templates. Anyway, visit these sites for starters to see if they're what
you're after.
Also, you didn't mention your level of expertise - beginner, novice,
moderate, pro, expert?
All the above come with comprehensive "How To" manuals or online resources,
bulletin boards, email support.