You can duplicate an existing base that you've already created in Airtable in one of two ways.
First, you can duplicate a base from the homescreen by mousing over the base icon, clicking the dropdown menu button, and selecting the Duplicate base option.
Second, you can duplicate a base from within that base by clicking on the dropdown menu arrow next to the title of the base, then clicking the Duplicate base option.
In either case, clicking the Duplicate base option will bring up a dialog that will allow you to choose the workspace into which you'd like to place the duplicated base.
By default, duplicating the base will create a copy that has all the records and comments in the original base.
You can toggle off the Duplicate records option to create a base copy that will have just the table, field, and view structure of the original base, but none of the records.
If you are choosing not to duplicate the records for reasons of data security, please be aware that your table, field, and view structures may also contain sensitive data (e.g., table names, field names, names of dropdown options in a multiple select field, etc.), and that simply not duplicating records may not be enough to create a completely "clean" copy.
You can toggle off the Duplicate comments option to create a base copy that will not have any of the comments from the old base.
Note that if you duplicate a base, the new base will not have the revision history of the old base.