Maybe you need to slow down and get to those books, or go through videos produced by Adobe's Julieanne Kost, LL , or George Jardine, to mention the three best series. Concentrate on what they say about catalogues and organization and try not to be distracted by stuff about Develop and Print.
Make sure you know where your catalogue files are and how many you have. By default they are usually in Pictures/Lightroom. They are crucial as all your Lightroom work will be in a catalogue file, and you need to be confident you know what they are. One shortcut is when you are in a catalogue - Edit > Catalog Settings > General > Show. Try it - it takes you into Explorer.
You can have multiple catalogues, but I'd strongly advise you not to do so. They are effectively breaking up control of your pictures and your workflow and as you've seen, you can't see or search in other catalogues. One catalogue can contains hundreds of thousands of pictures and performance isn't affected (the only effect is on time backing it up). Stick to one catalogue until you're confident you know what you're doing - and even then think hard before using more than one.
I'd also recommend not using your folders to categorise your work into countries or themes. Stick to one of Lightroom's default-date based folder structures, and use keywords to categorise your pictures with terms like America, Patagonia, Cowboys etc.