How to add background link & save changes

Hi my name is Larry Roederer I really need your help. My website is https://www.thetennistips.net The site really looks naked because It does not have any pictures. I added the plugin responsive full background. I did upload It and activated it. Can you tell me how to do the next steps. I need to learn how to add my background link the save changes Then I need to make sure. I can make this a beautiful background. I also need to learn how to add a picture to my header. When I first started I tried to add some Tennis pictures to my site. When I went to a site that offered free pictures I would right click. I do not no why It would not have save as at this point. I really appreciate all your help. Larry Roederer [email moderated – the forum does not provide support via email]