[How to activate a furniture add on]

I had to restart my computer, and then the add-on was automatically updated. 
Thank you very much for your advices! 
Wes, is that the site you were talking about? - https://3dwarehouse.sketchup.com/

 

[How to activate a furniture add on]

Hello. 

I'm studying Interior Design. I didn't have a built-in options to add a furniture in my project, so I downloaded one from here. But I can't activate it. I want to place some tables, a sofa, I want to change a table color and so on. 
Please tell me how can I fix this? 

 

Thank you in advance!
- Bobby