The create lineup has 4 different buttons on it -- here is an explanation of these buttons.
cancel --> leave the create lineup page & save nothing
save as draft --> save the lineup (even if only part of the lineup) - only visible to captain, co-captains, coaches and team manager
Submit Lineup --> save the lineup - only can be submitted when all the details are filled in. The whole team can see the lineup now for this given match.
Submit Lineup & Create Confirm Email --> same as "submit lineup" and after clicked you are taken to a new page to create an email for the team which is a "confirmation email" for each player in the lineup.
Traditionally the captain will want to use "Submit Lineup & Send Confirm Email" which will save the lineup and take you to a page to compose your email. Why use "match confirmation email"? As team captain it gives peace of mind knowing that X player knows they are "in the lineup" and they are confirming they will be there.