hide a category from homepage

I want to hide a particular category from displaying in the home page posts. I want that category to display in the sidebar and i have done it successfully. But i dont know how to hide it from the homepage.

In the forum i found that we have to edit the index.php
I trid Appearance -> Editor
There i find many different templates, but index.php is not available

P.S. I didnt install wordpress in my laptop yet. Using it online.
& I have no knowledge about codes.