From your Frontpage: 'This frontpage is an example of what you can do with this template. The sample content is just that, sample content. Included in this site are several tutorials to help you set up your joomla site in a similar manner as this demo'

The site you show and the template you've chosen are very similar.

The process is pretty straight forward even if you are new to Joomla.

It's just a matter of publishing your content to the correct module positions.

You'll need to create:

Sections, Categories, and Articles for the main content.

Menus for navigation

Modules for the side bar content.

You can

A) Edit the content of the demo template as it stands.

B) Delete the demo content for modules and positions you don't need, adding and editing where necessary.

C) Create another database, and use the rocket launcher to install Joomla and the template without the sample content, keeping the current install as an example.

IMHO, A & B are more difficult. Its always harder to edit a site that's already set up. You'll almost always miss something and some sample content will inadvertently pop up on one of your pages. You see it all the time on Joomla sites that are built off a sample data install.

For me, C is the best choice. You can work with two browsers open switching back ad fourth between the sample data and no sample data sites. This way you can add just your content and place it exactly where you want. And, in the end, there'll be no sample date, articles, links, modules, etc. that will surprise you later. 

how do I change round corners of modules to straight corners?

>>> I don't know much about thet template, but as with the others, I think it involved editing the source files.

how do I change both background and module colors, to the same color of other website?

>>> Check to see what color variations come with the templare. Chances are there wont be an exact match.   You'd have to edit the temploate files to get the colors you want.

Also, I do not know how to make toolbar menu like other website's menu. it is split and when you drag cursor its color changes.

>>> That may not be an option in that template. Of course, anything is possible if you want to custom code it.

Have you taken a look at the Chromataphore template?

It'd solve all the issues you mention above.

And once you get the colors exactly the way you want you can turn the color chooser off.

I just don't know if the template's layout / module positions suit your needs.