How can i install degital certificate/SSL on my web site?

First of all you need to purchase a digital certificate from any CA.When you receive your new Secure Server Certificate from CA, you need to extract it from the e-mail message and install it on your server. To do this:

From your e-mail program, save the Secure Server Certificate to a file, such as cert.txt.
Open Key Manager from the Internet Server program group.
Select the key pair that matches your new Secure Server Certificate.
Choose Install Key Certificate from the Key menu.
Select the Secure Server Certificate file you saved in Step 1 and click Open.
When prompted, enter the password that you specified when creating the key pair.
Choose Commit Changes from the Servers menu.
When asked if you want to commit all changes now, click OK.
Note: If you do not specify an IP address when installing your Secure Server Certificate, the same certificate will be used for all virtual servers created on the system. If you are hosting multiple sites on a single server, you can specify that the certificate only be used for a particular server IP address.
**Secure Server Certificate Installation Problems**
Due to a minor problem in Microsoft's Internet Information Server V3.0 and earlier, you might encounter a BAD PASSWORD error when attempting to install your Secure Server Certificate. Microsoft is aware of this problem and it will be resolved in the next release of IIS.
If you encounter this error, there are two possible solutions:

Solution 1

1.Paste the Secure Server Certificate into NotePad (not Word or Wordpad), including the lines containing the begin and end statements.
2.Remove any spaces between the left margin and the beginning of each line.
3.Add a blank line above the begin statement.
Add a blank line below the end statement. a line of
4.Remove any hidden spaces or hidden characters from the end of each line.
5.Select Save As and choose the "text-only with line breaks" file type and click OK. (The file should be named key.txt or cert.txt.
Follow the instructions above to install this new file.
Solution 2

1.Go into the User Manager.
2.Locate the Internet Guest Account and double click it.
3.Enter and confirm a new password. Make sure the password is eight characters or less and does not contain any symbols, such as: ~!@#$%^&*()_+).
Set the Password preferences so the password never expires.
4.Remove the check from the Account Locked check box.
5.Go into the IIS Internet Manager and select WWW Services.
6.Look for anonymous log on and locate the User Name (IUSER _ Server Name).
In the password field for this anonymous user, enter the same password you specified in Step 3.
7.Apply the changes.
Follow the instructions above to install the Secure Server Certificate.
***************Final Step Enabling SSL***************
Once you have applied the Secure Server Certificate, you must enable the SSL feature from the IS manager. SSL can be required on any virtual folder available in your web site and is configured on the Directories property sheet.
To enable SSL for a directory:

1.From the Management Console window,go to the web site properties.
2.Click the Directory Security tab.
3.Press the Edit button on the Secure Communication selection
4.Select the require secure SSL channel option.
Click OK