Open your journal at its edit page and look below the content editor for the References section. Select Add Reference to open its own dialog: choose a type, Webpage or Publication, and fill in the details. The only field the dialog actually requires is Title. URL, author and description are optional on either type, and even on a Publication reference, publisher, volume and ISBN are optional too. They only appear as extra fields because that type carries different citation metadata, not because the platform demands them. The one thing the form does check, besides Title being present, is a supplied ISBN: if you type one, it has to be 10 or 13 digits, hyphens allowed.
The number is your position in the list, not something you set
Each reference is numbered by when you added it. The first one you save is [1], the second is [2], and so on. There is no drag handle, no order field, and no way to move a reference up or down. The numbering always follows the order you created them in.
Getting the number into your text
Adding a reference to the list does not place a citation anywhere in your writing on its own. To do that, select the word or spot in your paragraph where the citation belongs so the inline toolbar appears, then choose the reference tool, the small button marked "R". It opens a picker listing your references by their current number. Choose one and it inserts the bracketed number, [1], [2], and so on, as a clickable citation at that spot. If you have not added the reference yet, the same picker has an Add New Reference button that opens the References dialog without leaving the editor.
Once inserted, the citation does two things. Hovering over it shows the reference's title, author and URL in a small card. Selecting it scrolls the page down to that entry in the References section and briefly highlights it, so you can confirm it points where you meant.
What you cannot undo
Deleting a reference asks you to confirm, and the dialog says plainly that the action cannot be undone. There is no trash and no recovery for a deleted reference.
There is a second, quieter effect worth knowing before you delete one. The bracketed number sitting in your paragraph is just a number, it is not permanently tied to the reference you originally picked. Every citation in your text is matched back to whichever reference currently sits at that position in the list. If you delete an earlier reference, every reference after it moves up one number, and any citation you already placed for those higher numbers will end up pointing at whatever source now occupies that position, not the one you originally cited. If the reference you delete happens to be the last one in the list, its citation simply goes dead instead: the bracket stays in your paragraph, but it stops linking and stops showing a tooltip.
If you need to remove a reference that is already cited in your text, delete the citation from the paragraph first, or check every citation number afterward to make sure it still points where you meant it to.