the last question is.... how can i reduce the size of title, remove the line under the title and reduce the space between title and tagline, when i enter in the single page...

That sounds like three questions. :)

Regarding the size of the font title, try using the size values for the site title on the Appearance → Custom Design → Fonts page first. Once you have selected any fonts on that page, very specific CSS is used to setup the rules for the site. To override them with custom CSS after that, you can use the "!important" rule:

.site-title h1,
.single-title h1 {
	font-size: 22px !important;
}

Here is some CSS for The Columnist theme that will help you hide the border under titles on single posts:

.single-title h1 {
	border: none;
	padding-bottom: 0;
	margin-bottom: 0;
}

Now, you have some CSS already saved in your CSS editor that is similar. You should remove those and combine everything for matching rules into one block like this:

.site-title h1,
.single-title h1 {
	border: none;
	font-size: 22px !important;
	margin-bottom: 0;
	padding-bottom: 0;
}

the last question is.... how can i reduce the size of title, remove the line under the title and reduce the space between title and tagline, when i enter in the single page....

best,

how can I add another column to the layout?

You can't really add dynamic content using CSS only, but sometimes what you can do is shift things around. Here is an example that would expand the main content area enough so that there is enough room for 5 posts to get stacked (floated left) in a row before they fall over to the next row:

#main,
#main:after,
.site-footer {
    width: 100%;
}
#content {
	float: left;
	width: 800px;
}

Try it out to see how it works, and experiment with the width values.

Another trick you can do is add a temporary border to the main content area and then preview so that you can get a better idea for how the layout works:

#content {
	border: 1px solid red;
}

i have another question...
how can I add another column to the layout?

thanks in advance.

reduce the space between site title and tagline

Add this to your Appearance → Custom Design → CSS editor:

.site-title h1 {
	margin-bottom: 0;
	padding-bottom: 0;
}

remove the line under the site title

Add this to your Appearance → Custom Design → CSS editor:

.site-title h1 {
	border: none;
}

I need to reduce the font size of site title

Try adjusting that from the Appearance → Custom Design → Fonts page.

thanks.