This is the yaml representation of a list of dictionaries. I strongly
recommend you to study the yaml specificiation [1], but this specific
example can be broken down as this:
"repo" is a variable. Since the elements that follow it start with a
dash, "repo" represents a list. Each dash starts a list element, and
all subelements in the same level of indentation are the part of the
same list element. So each group of "name", "url" and "key" belong to
the same list element.
Each list element is a dictionary. "name", "url" and "key" are the
keys, and after the ":" are their respective values. One way that can
help you understand a yaml document is to install the pyyaml library
and try to parse it with python: