[Tutor] What is this code doing? What is it?

[Matthew Polack]

We're beginners  trying to learn Python and have this sample code:

https://github.com/PySimpleGUI/PySimpleGUI/blob/master/ProgrammingClassExamples/Win10%20versions/2a.%20PSG%20(checkbox%20and%20radiobuttons)%20-%20Copy.py


There is a section of code that has this line::

result = str(' Cost: ' + '${:.2f}'.format(cost))

But I don't understamd what the curly brace part is actually doing:
{:}

'${:.2f}'

I think the 2f means to use 2 decimal places...but what does the rest of
this do?

..curly braces apparenly are for dictionaries...but I don't get how this is
a dictionary..or what this {:} command is actually doing?

Thanks for any clues or links to an easy to understand tutorial or
something on this feature.

- Matt

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