You can open the Components tray in SketchUp Make, and search the 3D Warehouse for what you are interested in. When you find something, click on its thumbnail (not the text description), and the model should appear in your scene.
That feature wasn’t working for a few days, but it is now.
The 3D Warehouse doesn’t support SketchUp 2017 and hasn’t for some time. The alternative to using the Components window is to use an internet browser to access the 3D Warehouse. From there download the Collada version of the file and import the included .dae file into SketchUp. Or use the web version of SketchUp to search the 3D Warehouse and download content. Then use Save as and save as a 2017 version to open in 2017 Make.
The browser that is embedded into older versions of SketchUp is not compatible with the security updates that have had to be added to 3D Warehouse. The page basically doesn’t work at all, not even the sign in that you would need to do.
You could use any browser to find and download the models, but to import those into 2017 you would need to download the file as Collada, then import that file. Even then it isn’t straight forward, the model downloads as a zip file, which you extract, and import the model.dae file inside the extracted folder.
The sign in to 3D Warehouse in a browser can be with Google, Apple, or a Free account Trimble sign in.