you describe how to re-categorize a web site, e.g. overwriting the category from "Business" to something else.
This COULD be a proper way to block a web site, but after you performed the steps above you need to ensure that the category you put the web site into is actually blocked in your policy and make sure that the extended list element you created is part of the URL filter setting that you use in your policy (out of the box there is one called "Default" which can be found under the "Settings" tab which is used. If you open it you will find options to select an extended list).
Which category you should choose in the extended list is something I cannot answer since I don't know which categories in your policy are blocked and which are allowed. I don't even know if you have enabled URL filtering, so I cannot make a good estimate which is the right category for you.
Rather than using the extended list you could add a rule which blocks the access to the web site. In the rule library you find under "Common Rules" a rule set called "Global Blocklist" which allows you block access to web sites specifically. Maybe this is a simpler option for you.
Seems we have categoty 3 as blocked.
But need to check with you how can i confirm that only category 3 is blocked?
Can we have block with more categories like category 3 and 4?
Also how i can check if url filtering is enabled?
you need to look into your policy and find the appropriate rules which are responsible for blocking. I don't know your policy so I cannot tell you where exactly to look. On a default installation there is a rule set called "URL Filtering" which contains all the rules for blocking URLs by category but generally MWG can be designed in any thinkable way so the rules might be anywhere in your policy. If you have not built the policy yourself you should first try talking to the people who designed the policy and find out where a block rule makes sense. If you need someone to look over your shoulder and help you with those steps I recommend talking to tech support for more in-depth assistance.
Generally you can block more categories yes. You are completely free in your decision what and how many categories should be blocked or allowed by MWG.