Can someone tell me how I can log on to my Mac without my password?

See this Apple note on resetting your admin password.

System Preferences->Accounts->unlock the lock->Login Options->set your account for automatic login.

Salient bit in the document that BCreg linked to:

Important: Passwords for administrator accounts should not be blank.

As noted above, If you have access to your computer. But that is a Very Bad Idea. That is how passwords get forgotten especially when you need to remember it.

What you don't like typing in a few letters when you start you computer? That also opens up the system from anyone walking buy and turn it on. It give them full acces to your private files.

Whatever.