As others have indicated, we need more information.
Some people access their email via a web page. If you do so, you should be able to log into your second account in exactly the same way that you do with your first account. i.e. go to the relevant log-in page and enter your username and password.
Other people access their email through a 'client' (which is a program specifically designed for the job, such as Outlook, Outlook Express, Windows Mail or one of the many others listed by Chuckfickens). The precise instructions on setting up your email account vary between the different clients, which is why we need further information from you.
However you'll need to know four things:
1. Your username. (For most accounts that's the bit before the @ sign in your email address, but some accounts require you to enter your full email address as your username).
2. Your password for the account.
3. The POP3 server address used by your email provider. (See below).
4. The SMTP server for address used by your email provider. (See below).
The POP3 and SMTP addresses you require will be on the support pages of your email provider. Alternatively (if you get your email through one of the UK's major ISPs) you can find them here:
http://www.idl.uk.com/email/isp_settings.htm
or here:
http://www.kitz.co.uk/isp/dns.htm
To set up a new email account in Outlook Express, go to Tools>Accounts>Add>Mail and fill in the information required by the wizard. Outlook is similar, as is Windows Mail.
Chris