What can you tell applications to do using AppleScript?

I know that you can use the tell application "" command in AppleScript to do many simple things like open a website in Google Chrome, play and iTunes song, or do keystrokes with System Events. Are there any other things that you can tell applications to do that might come in handy in some way? (I already know the iTunes and Finder tells... please don't include those).

There is a feature in the Applescript editor called the Library. it can be accessed through Window > Library on the top navbar, or with the shortcut Shift+Command+L. You can double click on the applications there, and you will see all functions, variables, etc.

The windows looks like this. Double clicking shows a new window with all possible functions, vars, etc for Applescript, and even Javascript and Objective-C. You can select those in a dropdown.

Data Types

In the window explaining possible actions, you will see a tag and an icon next to it. The icons represent the type. S stands for Suite, E stands for element, blue C stands for Class, purple C stands for class or collection, and purple P stands for property.

Say we have this example:

tell application "Safari"
set a to URL of current tab of first window
end tell

URL is a property of the type tab, current tab is also a property, but of the window. This is one way to use classes. The other way would be something like:

open n From the standard suite, this would open the object n.

AFAIK, Suites and elements do not have special treatment in Applescript

as @user3439894 mentioned in the comment section: If the application you are looking for is not in the library, you can open it's dictionary with Shift+Command+O, and selecting the app.

There is also a search for a certain keyword.

Let's say we want to learn how to use System Events to do press a key. If we search, we see that there is something called keystroke in the Processes Suite, and shows a description of:

keystroke v : cause the target process to behave as if keystrokes were entered
keystroke text : The keystrokes to be sent.
[using command down/‌control down/‌option down/‌shift down or list of command down/‌control down/‌option down/‌shift down] : modifiers with which the keystrokes are to be entered