When developing a NodeJS application in TypeScript you need the definition files for the modules you are going to use. To make it easier to download them there is a module you can install called tsd.
To install tsd:
npm i -g tsd
tsd you can type:
tsd install express
The above will create folders and a file in your project:
typings |- express |- express.d.ts
You can watch how to do it here: