Hi Vivek,
If you just enter 2 words in the Discover query bar with a space between them, you'll get results where any of the fields in the docs contain either of those words;
If you want to be specific on which fields should be searched you can list them (again with a space between);
So this finds docs where @message:uploads OR extension:jpg (the default is OR)
And this finds that meet both conditions; @message:uploads AND extension:jpg
Regards,
Lee