SketchUp has great resources and tutorials: https://help.sketchup.com/de/article/3000081
Export as STL
In order to 3D print your design, you need to get your file from SketchUp into Cura or another slicing program as an STL. You will need a plugin for this.
This page has a good, free plugin to export as an stl file: http://www.guitar-list.com/download-software/convert-sketchup-skp-files-dxf-or-stl
To install the plugin:
- Under attachment, right click "Download Sketchup to DXF/STL plugin - skp_to_dxf.rbz (RBZ file for Sketchup 2016, 2015, 2013, V8.2 up) - right click and save as" and save to your Downloads folder.
- In SketchUp, under Window select Extension Manager
- Click Install Extension
- and locate the skp_to_dxf.rbz file you downloaded above