If you'd like assets or collections to display in a certain order, say by filename or those most recently added, just select an asset section, then in Settings > General Settings, choose a sort order. Sort by the date they were added (oldest to newest, newest to oldest) or by filename (A to Z, Z to A).
Assets and collections in the asset section will sort in the manner you choose when editing the portal and when users view the public portal.
If you don't select a sort order, assets will sort by newest to oldest by default.
Note that if you sort by A to Z or Z to A, assets with numbers and symbols in the filenames will display first, then the rest of the assets based on whichever option you've chosen. As well, if two files have comparable filenames (e.g., FPO_ and fpo_), the file with the lowercase filename displays before the filename that's capitalized.
Sort assets and collections by pinning
Pin assets or collections in asset sections in order to give precedence and display them more prevalently for users. When you pin assets or collections, the rest of the assets/collections in the section will display in the sort order selected.
To pin, add assets or collections to an asset section, then click the Edit (pencil) icon. Click "Pin top assets" or "Pin top collections" and select assets or collections you want to give prominence to.
They'll display in numerical order as you pin them, but you can drag and drop them into the order you'd like. Click "Update" when you're done and the assets/collections will sort in the order selected. They'll display before non-pinned assets in the Live Editor and when you preview the portal.