An entry trigger (or ‘triggering event’) is the event that enrols a contact in a flow, e.g. contact abandons a basket, makes a second purchase, browsed a specific product, etc.)
Mouse-over the Trigger tile and select the cog icon to configure.
If you are mass uploading your contacts to a segment, be aware that the campaign won’t trigger to more than 1000 contacts at a time, and the remaining contacts will be ignored.
To avoid this, upload your contacts in batches of 1000 at a time.