Once you've invited a participate to your study, their status shows up as Invited.
For moderated studies such as interviews or focus groups, the participants are able to schedule time on your calendar.
In the example below, Jason is a invited participant:
Resend Invite - Once participants are invite, if they don't schedule time with you, you have the option of resending the invitation
Cancel Invite - If you don't want to view the participant anymore, you can hide them by clicking the "Hide" button. Here's a bit more on hiding the participant.
For Unmoderated Studies
Since unmoderated studies do not require a calendar and scheduled time, there is also the option to mark participants as either No Show or Attended.
See more on the other participant status here.