https://docs.mongodb.com/master/release-notes/3.4-reference/#pipe._S_graphLookup

1. First paragraph:

The stage matches the connectFromField of one document to the connectToField of other documents in the collection...

Should read something like:

The stage matches the values of the startWith field of incoming documents to the connectToField of other documents in the collection...

2. Description for 'connectToField' field.

Field name in other document against which to match the connectToField.

Should probably read something like:

Field name in other document against which to match the values of the field specified by connectFromField parameter.