Once you have your DCP, you need to get it to the cinema or theatre 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 that 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.
The “DCP-o-matic Disk Writer” provides a possible solution to this problem. It allows you to format and copy DCPs onto ext2-formatted disks from Windows, macOS or Linux.