Microflows which are modeled left-to-right. A microflow is a custom piece of logic, a “function” if you will. This can be anything from a validation flow, calculation, API calls, sending e-mails etc. Once a microflow is kicked off (by a user, or by a background process like a scheduled event) it keeps running until it's done. You can read more about Microflows here -
Workflows have a preferred top-to-bottom direction. A workflow is a way to model a business process. They are steps that are automatically paused when user input is required. They can also include microflows. You can read more about Workflows here -
Hope it helps!
Generally speaking, you can use workflows as a “process microflow” which can contain multiple microflows, as well as user input steps on pages (e.g., a Manager check) before continuing the process.
You can find the learning path here: https://academy.mendix.com/link/paths/112/Build-a-Powerful-Workflow, which contains a good explanation of what a workflow is and the use cases at the beginning.