When you installed WordPress, it should have asked you for your choice of a) admin username and b) admin password (Do not use "admin" as an admin user name and pick a secure password)
If you forgot what you put in for username and password, just use the installer to uninstall the WordPress and then just install it again remembering to write down the admin username and password (It should allow you to email all the info to yourself).
Also, if your entire site is going to be WordPress, I would suggest installing it in /public_html, not in /public_html/wp -- using the installer, leave the "directory" field blank. Then , instead of mysite.com/wp/ it will be just mysite.com/