You can find the Creative Cloud Libraries via the libraries panel in the window menu in Photoshop. You will then see the panel with all your current resources. They are all the files stored on the cloud, they are not on your local machine
The panel contains multiple themed assets stored in the individual themed (or in the case of mine, randomly named ones). It is basically a folder structure where at the top level you can see all the names.
Go to the top of the panel and enter some text in the search all field. You can also go into an individual section by clicking on the section entry and search that (magnifying glass). It is a good idea to name your assets when you create them and give them a sensible name. Probably OK to have them named background etc when you have about 10 or so items but when you have added thousands and thousands of entry, it is often hard to find a particular file without a good naming convention.
Below the search box there is a filter which is super useful as you can filter by type as well as library if you wish
They can also be sorted by date as well as name.
You can go to a particular section and invite people to check out the designs to (to be honest, not sure I will ever use that feature but if you are part of a team, it is of use I am certain)
You can create a new library at any time and it is great to add multiple new content to the creative cloud, so much easy to organize things Click the + create new button on the panel and you will then be able to add new content to that or move items from other sections. Remember to give it a good name, so much easier when you come back to it in a few month's time.
You can do it a few ways. Drag the resource into the panel (not everything can be saved this way) or go to the '+' at the bottom of the panel and select create from image, foreground, graphic etc. If you have a lot of shapes selected then click the + add all and they will all be added to the panel but all as a single arrow set which is not so useful. You can also drag individual items to the panel and they will be saved as a cloud object and they end up looking like a pixel object, they are basically a smart object which you can access and if you are using a custom shape, the custom shape vector design is still there, you just need to be able to double click the item in the layers panel to access it. A little fiddly. When you drag an asset such as a shape into the panel, a '+' will appear before you drop it and it will say the format such as 'layer'. All these designs are stored on the cloud. You can drag layers, you can drag all kinds of designs into the panel and they will all be saved in the current section.
Personally, the best format to store is a smart object as the smart object can have all the smart filters, adjustments, shapes, brushes, styles, type enclosed and that will then reside in your library and can b dragged back at any point to be used in new projects and all the component assets are still available and can be expanded.
OK, you have added them and that is super useful but how to use them later. You can drag them back in to the document, any document, in Illustrator, After Effects etc and of course, Photoshop. The design is linked to the creative cloud library so any changes you make to the smart object etc (the resources themselves) will be reflected in the panel. If you re-color the design etc that is not updated in the panel. If you look at the design dragged from the panel, you will notice that it is a smart filter. You will see any adjustments or effects added to it do not change the design in the panel, only on the art board and the layers panel will display the smart filters and adjustments etc. You can modify the design by double clicking the entry in the layers panel and then editing the PSB document and any changes will be reflected in the entry and on the art board
You may create a design that you want to edit but you don't want to change the CC version, well you can hold down the alt or option key when you drag the item and that will create a design that is not linked back to the panel. If the asset was originally a custom shape, the new design will still be a custom shape and you can edit the points etc using curvature tool, direct selection tool etc
Say you have a shape etc and you have a fill / stroke color that you really like and you want to save it, go to the + at the bottom of the panel and select the fill / stroke color option and it will be saved
There are a number of options that you can use if you have an object selected and you right click an asset in the panel / stored in the cloud. The menu depends on the item selected so if it is a color. If it is a graphic, the list will be different (though some things are the same such as duplicate, add to, description, copy to etc)
The duplicate and copy to etc and rename are useful to changing and moving items around the panel. You can also add a description up to 130 characters.
You can also use the place embedded as well as place linked, the place embedded is the same as alt / option drag
There is also a super menu on the right side of the panel. Where you can create new one, import one, export them as a cclib format and you can then import it later or perhaps for a client etc. You can invite people to check out your contents, you can rename them etc and you can also view all the designs on a website (it is a cloud service). There is also the useful learn more and what's new and even more important, provide feedback (I love that kind of feature as I have tons of suggestions that would be useful for me but perhaps no one else)
There is now also a group structure inside the library structure (personally, I think it over complicates things) and you can create an initial group, you can also select an item and right click and create a group from that. You can also go to the group and right click and create a subgroup and right click the subgroup and create a subgroup for that. You can ungroup and also you can move items from groups into sub groups by dragging and dropping. If it is not grouped it is in a section called 'not grouped'.