A manual transmission (also known as a manual gearbox; abbreviated as MT, and sometimes called a standard transmission in the US) is a multi-speed motor vehicle transmission system, where gear changes require the driver to manually select the gears by operating a gear stick and clutch...
In this case, the 6 (in 861) means that it has a five-speed transmission with a three-point hitch and a non-live PTO. The third number, in this case 1, tells us that this is a 1 series tractor built between 1958-1962. For a complete list of these numbers and what they mean, get a copy of the Dennis Carpenter 1939-64 Ford Tractors catalog.