Exporting photos into a new
Catalog
Whilst it's possible to export photos into a new catalog
from any one of the Lightroom Classic modules it is visually much easier if done from
the Library module Grid view. So, the first step would be
to switch to the Library module, as shown in figure 1.

Figure 1 - Lightroom
Classic Library Module
Next, we identify the folder or folders containing the
photos that we want to export into the new catalog. In the example shown
in figure 2 below I have chosen a folder named Iceland 2018,
but it could equally have been two or more folders / subfolders. When exporting an
entire folder, it isn't necessary to select the actual photos, just the
containing folder. That being said, it may be that you only want to export a
small selection of photos from one or more folders. Fortunately,
Lightroom Classic is flexible enough to allow both.
Tip: to select multiple folders - click on
the first folder then, while holding down the Cmd (Mac) / Ctrl
(Windows), click on the other folders that you want to be included
within the new catalog.

Figure 2 - Selecting a folder
Having selected the folder(s) that
you want to
export
to a new catalog you then choose the Export as Catalog command from the
File menu (figure 3). The Export as Catalog dialog will open. Note
that there is no keyboard shortcut for this particular command, however,
it is possible to create one or remap an existing shortcut using the
method described in this linked
tutorial.

Figure 3 - Choosing the Export as Catalog... command
The next
step is to give the new catalog a name and define the content. But before
doing so it's worth describing what each of the three options in the
Export as Catalog dialog (figure 4) does.
Export selected photos only
When this option is checked only the photos that have
been selected in Grid view will be exported to the new catalog. However,
be aware that this option simply exports the metadata (e.g. IPTC, EXIF,
keywords and any develop settings) associated with each photo into the
new catalog, the actual files (negatives) will not be included. In some
instances this may be all you require, but in others it may be important
that the actual files are also included. We'll address this latter situation in
a moment. Typically, this option is only used when you need to export a
small subset of photos from a folder or multiple folders. Leaving it
unchecked is important if you want the new catalog to include all photos
within the selected folder(s).
Export negative files
With this option checked Lightroom
Classic will export a copy of
each raw file into the new catalog. If the photos include Virtual Copies
and/or sidecars these too will be included in the export. Likewise, any
PSD, TIF or JPEG files that are contained within the selected folder(s)
will also be exported. This option is generally used when the new catalog
is to be transferred to a new computer, stored on an external or disk or
DVD, or shared with a third party.
Build / Include Smart Previews
With this option checked Lightroom Classic
will include Smart Previews for each raw file in the new catalog.
Smart Previews can be used in lieu of the original raw files when
the original are off-line. Lightroom Classic can also be configured to
utilise them to improve editing performance.
Include available previews
With this option checked Lightroom
Classic will include all
available previews for each of the photos included within the export.
Typically, these will include the thumbnails, standard-sized and, when
available, full-sized previews. If this option is left unchecked
Lightroom Classic will need to render the previews when the new catalog is first
opened. For this reason, it is very important that this option is checked
in situations were the negative files are not exported to the new
catalog.

Figure 4 - Defining Catalog content
The example shown in figure 4 above is ideal for
situations when you want to create a small catalog of photos that
you'll copy to another computer for editing whilst 'on the road' or for
'archiving'.

Figure 5 - macOS folder view of new Catalog
Figure 5 shows the
macOS folder view of the exported
catalog described above. Notice that it it contains two files (i.e.
the lrdata preview file and the lrcat catalog
file) and a folder. The folder contains the exported negative files.