Right click on the gray field and choose node type
Left click on the light-grey arrow part of your node.
To create a query - just create new type and set it from right menu as query.
On the right click you can set up array or required for selected node.
To create a mutation just create type node and choose from right click menu mutation
To connect nodes grab arrow on light grey side of your node and drag it to the same part of another node.