Projects are the main hub for your client interaction. Think of it as a file folder for your client. A project holds all the client's documents including lead capture forms, quotes, questionnaires, invoices, contracts, emails, etc. It also stores your workflows, and displays your project's lifecycle.
Workflows are pre-written to-do lists, that each of your projects always need to complete in their process with you. These "To-do lists" can come pre-set with your templated documents and emails that you want to send as well. These can be added in your workflow as "Action" items. Learn more about workflows here.
Lifecycles give you a visual representation of where your project is at within your overarching process.You can read more about the difference between lifecycles and workflows here.
It’s important to note that you do not have to create both a lifecycle and a workflow although they can work together. A lifecycle does not have to follow the steps of your workflow or vise versa. They are completely separate and you can build them in any fashion that meets your needs.