At the moment it’s unfortunately not possible to use community nodes on cloud - only on a self-hosted instance. There’s a feature request you can upvote here: Community Nodes in n8n.cloud
There’s also a Docusign node request here (which leads to the Docusign community node, which may be where you saw that a community node exists?): Docusign Node
I’ll also ping @Niklas_Hatje on this one about the possibility of community nodes coming to cloud 
I haven’t worked with Docusign’s API before, but I believe what you’re looking for would live here: Envelopes Category | REST API | DocuSign That being said, since Docusign is a pretty complex product, I wouldn’t know for sure 
There may be someone else on the forums with more direct experience.
From there, you can use a HTTP Request node to authenticate and make the request 