An idea becomes easier to challenge when someone can run it. On January 8, 2009, at 19:27:40 UTC, Satoshi Nakamoto announced Bitcoin v0.1 to the Cryptography Mailing List. The archived message provides a download link and says the package includes C++ source code. The release announcement.
Three beginnings, not one
The white paper was announced on October 31, 2008. It explained a proposed system. The original mailing-list message records that publication; it does not mark the launch of public software.
The genesis block records January 3, 2009 in its header. That is earlier than the public release announcement. Keeping these dates separate avoids making one event stand in for the entire beginning of Bitcoin.
What early users received
The v0.1 announcement describes a Windows application that could connect to peers, receive payments, and generate blocks. It also explicitly calls the software experimental and leaves open the possibility that the system might need to restart. This was an invitation to test a new design, not a promise of an established payment service. What Satoshi announced.
Read the instructions as history
The message describes features and expectations of the original release. It is not a current installation guide. Bitcoin software, mining conditions, and recommended operating practices have changed since then.
To follow what happened next, read about the first transfer to Hal Finney. To separate the proposal from the implementation, start with the white paper’s publication.