Commands of a block will have same indentation level, you could have multiple block levels in a source file. Just like python.
To understand better about block, please read bellow sections about if structures and loop structures and functions.
Indentation level depends on number of spaces and tabs at the beginning of the line contain the command
Indentation level = round( number of spaces/4) + number of tabs
Blocks of commands are multiple commands that is expected to be executed together, executed in order top to bottom, left to right.