Not able to create the authorization request.

Hello, I have my client id, client secret and the redirect url. 

But here in the api documentation, the url of authorization request is like this ->

https://authz.constantcontact.com/oauth2/default/v1/authorize?client_id={your_client_id}&redirect_uri=https%3A%2F%2Flocalhost%3A8888&response_type=code&scope=contact_data%20campaign_data%20offline_access&state=235o250eddsdff

I am not able to understand the state option here? What does it mean? Where can i get the value from?
Also what is the redirect url conventions? 
Please share some insights, I am stuck.