You simply get a copy of their library, either the commercial or the open source one. For open source, I built my own copies today for Mac and below you can download them. When you use my SQL plugin functions, you normally set option to point to libsqlite.dylib file. But instead to this file, you point to the libsqlcipher.dylib file. Now you run as first command "PRAGMA key = 'passphrase';" to pass in your password for the database. All following calls should run normal and the file is encrypted.
This is not the same encryption as used by Xojo. They use the SQLite Encryption Extension from Hwaci - Applied Software Research (see hwaci.com/sw/sqlite/)
Download my built library: sqlciphermac.zip