Command Prompt – Log in as the root user

I have just started studying MySQL from an O’Reilly book. Having now installed and configured MySQL, the book prompts me to open a shell (ie the command prompt) and then login as the root user mysql -u root -p, at which point I will be asked for the root password. This is one of several steps required before I can create a database.

Not sufficiently familiar with using command prompts, I am having trouble on this particular step. Can anyone please give any guidance?