How can I add text in my theme? Drupal is a complex CMS but all I need is simply a text on my page in the specific region of the page ( that will be rarely changed ) that can be changed by an admin.

Here's my theme mockup. 



The text is going to be in the red square area as seen above. That text is going to be rarely changed. I was trying to do this with 'Basic page' content type block but It isn't showing me what I want it creates some text showing up 

"No front page content has been created yet. Add new content"

and when I create new content It shows up Read more and then redirects me to node/1 URL If I click it.

There must be some other simpler way of doing this. I mean all I want is text that is editable by admin in control panel not some fancy blog posts. Also please notice that I am still learning Drupal and any answer would be great!
By Default Drupal front page shows the list of Contents you create, the number of contents you can list is controlled in Site Configuration. To answer you particular scenario would be too much of an answer here, I'd recommend you to read some Beginner Documents or watch some Videos in the net. Good place to Start is Drupal documentation

To displaying content in front page go-to UR-URL/admin/config/system/site-information and change the default front page to node/1 (in your case). This will display static front-page when your created the Basic page. 

Be aware this is not the best bet, so, I'd suggest you to explore Drupal bit more before actually starting the site building.