If you installed the Nuxeo CSV add-on from the Nuxeo Marketplace, you'll probably want to enable CSV import on the document types you defined, either in Studio or with some code. Here is how to do that.
- In Studio, on the left side, under Configuration, in the Advanced Settings menu, click on XML Extensions.
- Click on New to create a new extension.
- Give it an ID and click on Next. - You may want to check the Studio naming conventions. 
- Paste the following content in the text area and fill in the - <type>tag with the ID of the document type on which you want to enable CSV import.- <require>org.nuxeo.ecm.platform.actions</require> <extension target="org.nuxeo.ecm.platform.actions.ActionService" point="filters"> <filter id="importFile" append="true"> <rule grant="true"> <permission>AddChildren</permission> <type>YourCustomTypeID</type> </rule> </filter> </extension>
- In the XML extension, put as many - <type>tags as documents types on which CSV import should be enabled.
- Click on Save. After you update your Nuxeo Platform instance, your document type(s) will have the Import a CSV file button.
If you don't want to use Studio and prefer using your IDE, you can just add a contribution with the XML above.