Referring to variables in bash

Question

Is there a difference when variables are referred to as $variableName and ${variableName} in bash?

Answer 1

From man bash:

The basic form of parameter expansion is ${parameter}. The value
of parameter is substituted. The braces are required when
parameter is a positional parameter with more than one digit, or
when parameter is followed by a character that is not to be
interpreted as part of its name.

Examples:

echo ${10}
foo=bar
echo ${foo}bar