Question about LO Writer and "complex documents"

users
#1

Maybe someone would be so kind as to explain the difference between
.ODT & .OTT;
          when is the latter used & how does it differ?

#2

ODT (OpenDocument Text) = Writer Document
OTT (OpenDocument Template) = Writer Template

Opening a OTT file in Writer will create a new blank ODT document with
the attributes/styles contained in the OTT template. The OTT template is
not altered by anything added to the new ODT document.

An ODT document can be used to create an OTT template.

Suggest you read the "Styles" & "Templates" chapters of the Writer User
Guide for more detailed information:
https://wiki.documentfoundation.org/Documentation/Publications