These tabs, accessible from the Capture settings button on the Toolbar, or from the Capture menu item, Capture settings, define the default settings the program will use when you execute screen captures. This section of the help explains each item for the tab set in the order it appears in the tabs.
Before you change a default operation, please make sure you're clear on what that function does and how it will change the way in which the program works. Jot down a note on what you've changed, in case you don't like the results and want to change them back.
As always, the best way to discover what something does is to examine it, change the setting, and re-capture the same screen or window and see how it differs from the previous setting's results. Experimentation will always be the best way to learn what something does, as long as you remember what you changed and what it was previously in case you don't like how it came out.
You can access some of the settings during post-capture processing (for example, cropping and scaling).
Click on the names of each tab displayed to the left to view help about that tab in the pane here.