There are many aspects of a Marketing Cloud journey, and we encourage you to review the Journey Builder documentation. When using the Omnichannel Connector app, the most relevant components of a Marketing Cloud journey are:
The entry source establishes the customer information and circumstances that trigger the journey. Messaging activities can automatically send messages to those customers, and flow controls direct the customer along the paths of your communication plan based on the information provided throughout the journey.
The Omnichannel Connector app provides you with an entry source type (and corresponding data extension), messaging activity, and flow control activity that allow you to make use of the Conversation APIs functionality in your journey:
While this article provides a high-level overview, you can visit our developer documentation for the Sinch Omnichannel Connector for Salesforce Marketing Cloud for more in-depth information and reference material.