The description of your website is displayed on search engine results pages, and is a concise explanation of your website's content, so it can impact click-through rates however they aren't used by the search engines to determine your rank.

Try to limit it to 150 characters (space too, is considered a countable character), which are most descriptive and relevant to your website. Avoid repeating words (do not repeat any word, more than twice), because it will not help you at all.

To change your website description:

Step 1:
Click on the Settings Tab.

Step 2:
Select Website Settings from the menu drop down list.

Step 3:
In the Description field enter your website description.

Step 4:
Press the Save button to save your changes.