What is the use of sign up?

What is the use of sign up?

Sign up is a verb phrase. It means to enroll or register for something. One might sign up for intramural sports, a parent-teacher conference slot, or health insurance.

Is it log on or log in?

Log on is also a verb phrase. When you log on to something, you are simply accessing digital material, without necessarily needing to provide credentials. When you logged on to this site, for example, you did not need to provide a password to read this article.