I know this has been asked, but I'm compture illiterate and just need some help

My "mobile downloads.lrdata" is effectively killing my macbook. I can't do anything on it since it is taking up 123.15 GB of space. You can choose a different location for your mobile files to download to in Preferences > Sync > Choose Location.

I use LR Classic (now LRC). And I use the creative cloud program so I "believe" that all my files are on the cloud, in lightroom's storage area. So I don't know how to change having all these files in mobiledownloads.lrdata. Needless to say I am deathly afraid if I delete them that I'll lose them and I don't want to do that. No, if you are using Lightroom Classic your images are not 'on the cloud'. Lightroom stores your images in the cloud. Lightroom Classic stores your photos where you choose. If you haven't designated a location for your images then by default Lr Classic is storing them on your local drive in your Pictures directory–you can see this by navigating to and opening that folder at the system level. If you aren't using an external drive you will eventually run out of room on your local drive depending upon the size of your drive and how many images you import. If you want your images to be stored in Lightroom's cloud server then you may want to use Lightroom instead of Lightroom Classic. You have to evaluate the tradeoffs and decide where you want your originals and what features are most important to you. As you've noted you are running out of space on your hard drive so moving them to an external drive is a necessity.

In looking at my folders in lightroom I can see the folder that has these images - it's in "Jack's Macbook Pro" under imported photos. I would think this would be as easy as moving this folder to my cloud folder - but I don't see that. I see my iPad folder (hardly used), my iMac, my iPhone, and I see lightroom web. In Lightroom Classic,  when you select a folder, right-click and Show Parent folder you will see that the folders are in your Pictures folder. Another way to do this is to right-click on an image in the Library module and select Show in Finder and that will open the folder's location. If you simply drag your folders from your Pictures directory to Creative Cloud folder your originals will still be on your internal drive taking up disk space and also in the Creative Cloud. The only way to free up the space you are utilizing with your photos on your drive is to move the images to an external drive. To have your Creative Cloud folder show up in your side bar you need to drag it to the side bar from [Mactintosh HD> Users> name> Creative Cloud Files. Keep in mind that the contents are in both places and this will not free up space on your drive.