ERROR 1045 (28000): Access denied for user ‘root’@’localhost’ (using password: YES)

I have been following a manual to install a software suite on Ubuntu. I have no knowledge of MySQL at all. I have done the following installations on my Ubuntu.

sudo apt-get update
sudo apt-get install mysql-server-5.5
sudo apt-get install mysql-client-5.5
sudo apt-get install mysql-common
sudo apt-get install glade
sudo apt-get install ntp

Then I do

cd ~/Desktop/iPDC-v1.3.1/DBServer-1.1
mysql -uroot -proot <"Db.sql"

I ended up with the following error message.

ERROR 1045 (28000): Access denied for user ‘root’@’localhost’ (using password: YES)

How may I fix it and continue?

Note: For MySQL 5.7+, please see the answer from Lahiru to this question. That contains more current information.

For MySQL < 5.7:

The default root password is blank (i.e., an empty string), not root. So you can just log in as:

mysql -u root

You should obviously change your root password after installation:

mysqladmin -u root password [newpassword]

In most cases you should also set up individual user accounts before working extensively with the database as well.