You can read all about CaseComplete integrations with Enterprise Architect and TFS here: https://casecomplete.zendesk.com/hc/en-us/sections/200175477-Integrations
You can import a CaseComplete project to Enterprise Architect; this handy video shows the steps to do that: https://casecomplete.zendesk.com/hc/en-us/articles/200685087-Sparx-Enterprise-Architect-or-other-UML-design-tools
Requirements.cc is free and you do not need CaseComplete to create an account or to review projects, items, or polls shared with you. However you do need to have CaseComplete in order to upload your own projects, and you can upload as many projects as you want!
There is no direct way to import a diagram from Enterprise Architect to CaseComplete, but if you can export your Enterprise Architect diagram as an image file (png, jpg, etc) then you can import that image into a CaseComplete diagram or add it as a related document.
All of our training videos are online and you can access them here: http://casecomplete.com/learn