Once you have your DCP, you need to get it to the cinema or theater who will play it. Sometimes this is possible via the internet, using a service such as Filemail. If that's an option: go for it! Network transfers avoid a lot of the difficulties that other methods have.
However, your DCP may be too large to make that practical. In that case, the usual approach is to copy the DCP onto a USB hard drive or stick and physically take it or send it to the cinema.
In theory, this should be as simple as dragging and dropping the DCP's files onto a USB-connected drive. Sadly, though, things are not always this simple. This is because not all hard drives are formatted in the same way. The most common formats for hard drives are:
You can format a drive however you want, but a drive set up on macOS will usually use APFS, just as one set up on Windows will probably use NTFS or ExFAT.
The problem you have as a DCP maker is: the only format that is guaranteed to work in all cinemas is ext2. This format is not easy to use directly from Windows or macOS: both operating systems need extra software to write ext2 drives. So what can you do?
This may seem a strange suggestion, but although it's true the ext2 is the only format guaranteed to work, the Windows format NTFS will also work correctly in most cinemas. If you are using Windows, your best option may be to format a USB drive using NTFS and copy your DCP onto that.
DCP-o-matic 2.16.0 includes a tool called the ‘DCP-o-matic Disk Writer’ which was designed to solve exactly this problem. With it, you can write data to ext2 drives from Windows, macOS and Linux.
FAT32 is a Microsoft format which is well-supported by both Windows and macOS. It can be a good option to use for your DCP drive, but it has one major problem: it has a low (4GB) limit on the maximum file size it can hold. If your DCP is longer than a minute or two it is likely to exceed this size.
Whatever you do, there are few things that you should avoid: