Automate is a tool that lets you connect and automate applications. With it you can design and manage automation workflows between these applications without writing any code.
Zaps are the automated workflows you create. A single zap contains all the different applications that you have strung together to automate a task.
Apps are the programs you want to string together to automate a task. You can combine and use these apps in different ways to automate any repetitive tasks. There are over a 1000+ applications.
Automate keeps a track of all the history of zaps that were run in the past. You can click on a task that was run in the past to audit it or run it again if it failed.