To export a family tree from Family Echo, please use the 'Download/export this family..' button in the bottom of the left hand panel. You should see a list of different file formats you can export your family tree information in.
To import a family tree, please click 'My Account' in the top right of the page and then choose 'Create or import a new family'. You can import GEDCOM or FamilyScript files into Family Echo.
I'm not sure what you mean by link to different family tree, please could you add info to the question or in a comment.
