So this below is the output from running gulp serve - what do I need to do to get it running?

M:>gulp serve module.js:549 throw err; ^

Error: Cannot find module '@microsoft/sp-build-web' at Function.Module._resolveFilename (module.js:547:15) at Function.Module._load (module.js:474:25) at Module.require (module.js:596:17) at require (internal/module.js:11:18) at Object. (M:\gulpfile.js:4:15) at Module._compile (module.js:652:30) at Object.Module._extensions..js (module.js:663:10) at Module.load (module.js:565:32) at tryModuleLoad (module.js:505:12) at Function.Module._load (module.js:497:3)