You're not being too clear as to what exactly you want to do. Please be more specific as to what your problem is.
To get the MD5 hash, use:
string mhash(int hash, string data)
Example:
$MD5_hash = mhash(MHASH_MD5, "Password");
print "The MD5 hash for \"Password\" is '$MD5_hash'.";
If you're not sure how to make a form, review basic HTML regarding forms. Then use PHP to apply it to your form. (Don't take this as being rude, but you must learn to walk before you can run). When you figured out how forms work and you're still having problems, resubmit your problem. 😃