You build the graph from right to left (unusual but ok), but if you try to actually draw your lines from right to left they don't connect, you have to draw them left to right.
To rename something you click the element and type the name. Fairly straightforward, except that the interface gives no indication that this is possible. No blinking text cursor or anything of the sort.
The "arguments" category actually has nothing to do with arguments, it's just "use stuff you named previously". Why is that not something that's connected on the graph?
Oh, right, that's because of the way queries/mutations work. The name of the query is combined from the name of the query node and the name of the output node. But instead of a query having two connectors, one for input and one for output, it just has everything at a depth of one as outputs, and the child nodes of the output are the inputs (actually, that's how types and everything else works too). I certainly wouldn't have guessed that.
Compare Blender's node editor: https://code.blender.org/wp-content/uploads/2012/01/node_gro...
Anyone can look at a screenshot of Blender's editor and knows what's going on: labeled connectors, no magic with different layers, etc. Creating them is also straightforward. In comparison, if you show a graph from this tool to a random developer that works with GraphQL he/she likely won't understand what schema the graph is supposed to represent.