In Sharepoint there is no such username and password, by default username and password in sharepoint is stored in Active directory.

You can modify username and password in active directory, refer below post.
www.go4sharepoint.com/.../...3-sharepoint-168.aspx

Based on your questions it seems you have recently installed sharepoint 2010 on your system and has forget password

1) What is website URL for my recently created sharepoint 2010 website?
Answer:
your computer name is URL for your sharepoint website. Example: http://YourComputerName You can also type http://YourComputerName/SitePages/Home.aspx

In order to find name of your computer Open windows explorer > Right click on Computer > Choose properties from popup menu, and you would able to find your computer name.

2) How can i know what is username?
Answer:
Username to access sharepoint 2010 website is same as username you are using to login into your computer system and your password will also be same as you are using when you are trying to login into your system.

3) Can I reset password, if yes, how can i reset password?
Answer:
Yes you can reset password, with the help of Active directory.

4) Is there any option like forget password in sharepoint 2010 website?
Answer:
To best of my knowledge there is no such option like forget password in sharepoint 2010 website.