Automations → Action Credentials lists stored credentials (Name, Type, Created) with a filter by name and type.
Creating
Name, Type (generic, webhook, HTTP request, chat message; only a label), URL, Webhook URL and a Signing secret. The secret is stored encrypted and cannot be shown again. The secret is used only to sign webhooks; an HTTP request ignores it.
Using one
A step references a credential by its id (the credentialId box on the step), but the table has no id column, so in practice there is no way to find it on screen. There is no edit and no rename: replacing a value means deleting and creating, which gives a new id and breaks every step that used the old one.
Deleting
After a confirmation. A step that still refers to it fails with "Referenced credential not found". Typed tokens in a step's config are kept in plain text and in run snapshots; use a stored credential where you can.