How can I decrease the space between Menu bar Site description

You will probably need to start customising your theme’s CSS – possibly via a child theme. Try using Firefox with the Firebug add-on for this kind of CSS work.
https://getfirebug.com/

Look at the margins here:

#site-description {
    color: #7A7A7A;
    font-size: 14px;
    margin: 0 270px 3.65625em 0;
}

You’ll need to add the above selector and margin style — modified to your child theme stylesheet.

I have added the code in the style.css in my child theme but It did not work. Please suggest again.

Consider posting on a CSS-specific forum when querying CSS-specific issues.

There is no code like the above in your child theme stylesheet. Where did you add it?

If you have any caches, be sure to clear them.

Hi WPyogi. I am sorry to post the previous reply. However after changing the value 3.65625em into 1.65625em it worked. Finally thanking you for helping.

You have this:

#site-description { color: #FF8C00; }

so try changing that to this:

#site-description {
    color: #FF8C00;
    margin-bottom: 0;
}

EDIT — we cross posted — no problem and glad you got it working!

Thanks for help. However I see wide space in the left site both in the header and in main body section how can I do it into zero? Any help will be very appreciated.

You’ll need to look at the margins for both of those sections of the page (likely here: .left-sidebar #secondary and #branding hgroup). As esmi suggested, the best way to work with CSS is by using Firebug — it will show you the CSS that is affecting a specific area or element on a page. The firebug site has good documentation about how to use it. Learning basic CSS is not hard — just takes some practice. This is also a very good CSS reference:

https://www.w3schools.com/css/

Yes I will follow firebug. Thanks for reference. However I could not solve extra space from left and right site both from left and right.