Including and Excluding
The Send to step is the step in which you define your target Audience in the SMS and Email tools.
You will get the option to both include and exclude Segments when you're in the Send to step in both activities. On top of that, you get to decide if you wish to include/exclude profiles who match all or any of your Segments
Keep in mind that the content of your Segment determines the Profiles who are included or excluded from your activities. Included or excluded conditions and rows, as well as the AND/OR relation, are affected by this step.
To put it simply, excluding a Segment will invert both the conditions and rows as well as the AND/OR relations in your Segment.