Do I need to have a FamilySearch account to access the FamilyTree app?
Meaning the smartphone app? Yes, you need a FamilySearch account to do anything using the app.
@dontiknowyou provided the best answer to your recent question. If I may expand just a bit, many users have a member FamilySearch Account and a Church Account at churchofjesuschrist.org. Those who have both a Church Account and a member FamilySearch Account may have a different password for each account. If you wish to use the mobile app, you cannot sign into the mobile app using your Church Account login the way you can at the website. The mobile app requires the FamilySearch login. This can be confusing to those who have both the account at churchofjesuschrist.org and at familysearch.org.
I hope this helps you to remember which password to use if you want to work in the mobile app.
Latest update has changed this, so that you CAN use either your Church Account OR your FamilySearch Account login credentials in the FamilySearch Tree app.