This global section is related with the websites links and options value.
Click on Dashboard> Appearance> Customize> Global
Start editing Global Option
Options value lets you save the value of the page, categories, posts, etc. Sometimes your web page does not recognize text words. From here you will be able to save those text value to recognize in the web page.
Click on drop down option and select value as either slug or ID
Link option is related to the links of posts and pages of your entire website.
This section includes two types of links options. They are Outline on link focus and underline links on hover.
Click on Links
Disable Outline on links Focus
This option allows having out links when you right-click or only click on the pages or post links. It is by default and you can see the outline on links
Disable Underline Link on Hover
The option lets you have underlined in the page and posts links when you hover or point out. It is by default enable and you cannot see it but if you disable you can see underlined links.