Creating mappings

To start off, you'd could either match mappings from a certain version or map everything manually. Then, you'll need to get the mapping tool called Enigma.
You can get it from one of the following links:

• MCPHackers' MCPEnigma
• prebuilt jars of cuchaz's Enigma

After running Enigma, head over to "File" tab in menu bar, choose "Open Jar..." and open the jar of whatever version you're trying to map.
If you already had the mappings outputted by matcher, you could load these and edit them.