Usually in the web.config file you will find a section of code like this...
<connectionStrings>
<add name="ConnString" connectionString="data source = david-pc; initial catalog=database; user=typeyourusername; password=typeyourpassword;"/>
</connectionStrings>
setp 1)
where it says data source = david-pc
replace david-pc with the server name displayed on your login screen when you log into sql server management studio
step 2)
replace typeyourusername with the login value when you login to sql server management studio
step 3)
replace typeyourpassword with the password value when you login to sql server management studio
step 4)
replace database with the name of the database you created through the script you ran