Installed Pixel theme and tried to create an under construction page while I play and learn in the background. Not only did I 'not' achieve that - I managed to delete the header navigation and the base from all pages. I have gone to versions and it will not go back to the start. I've tried installing new themes but as I now realise all that does is change the look of the mistakes I have already made.
Basically I just want to 'start again' (how do I start over?) and then put up a holding page so I can mess things up in the background while I learn....
A good (and safe) way to learn your way in is to have one or more development or learning sites on which to make experiments and mistakes without breaking your main site.
For the holding page, you can put the site in 'maintenance mode' and visitors will see the maintenance page. Or you can install the 'under construction' addonhttps://www.concrete5.org/marketplace/addons/under-construction,... or you can put it on the home page, then use permissions so no-one but you can see anything else.
To show my complete ignorance, what is CLI?