You can check the syntax in Both mode to understand the structure better.
title
.section
.
gantt
title A Gantt Diagram
section Section 1
A task :a1, 2014-01-01, 30d
Another task :after a1 , 20d
section Another section
Task in sec :2014-01-12 , 12d
anther task : 24d
title
.section
.
gantt
title Project AAA
dateFormat MM-DD
axisFormat %m-%d
section My website
Plan : crit, done, plan, 05-15, 10d
Start working : active, work, after plan, 180d
Test : test, 08-01, 70d
section Programming
CSS:b1, after implement copyright, 30d
JavaScript :b2, after b1, 20d
Integration : after b2, 40d
section Design
Sketch: active, wire, 06-12 , 18d
Layout: implement, after wire, 24d
UX test: crit, uxt, after implement, 24d
section Blog
Blog writing: copyright, 07-29, 15d