Syntax and indentation

Indentation is the structure, not decoration.

Blocks are indented

Where other languages use braces, Python uses indentation. Everything indented under a line belongs to that line, and mixing tabs and spaces is an error rather than a style problem.

Four spaces per level is the convention almost everyone follows.
A colon ends the line that opens a block: if, for, while, def, class.

Comments and line endings

The # character starts a comment that runs to the end of the line. Statements end at the newline, so semicolons are legal but nobody uses them.