There are many areas from within Zapier you can create and view Zaps. But the main and easiest way is to simply click on the Create Zap button in the left menu bar from anywhere on the site. This will take you straight to the Zap creation page starting with a blank design.
Trigger section is the first part of any Zap automation. This is the section that represents the trigger of the Zap. You can add by choosing an app and then from its list of events. Each event may have other options available, some of which may be optional to specify the event in some way. Such as if it's an event for a new file appearing in a file system, there may be options to set which folder to watch.
Once you have your trigger, next is your action step under "Action". This is the same process as setting up the trigger, choose an app and then from the list of possible events. Likewise there may be other options to specify the action's details.
Only available in the paid plans, formatters let you tweak numbers, dates, and text in over a dozen ways to get it in the format you need. You tell it which data from the trigger step to work on and what it should output.
Only available in the paid plans, filters tell your Zaps to run only if your data matches certain criteria. You can treat this as a way to make the trigger more sophisticated than the actual events and options given in the trigger step.