1) Add the libraries that you want to use in your theme's compony.info.yml file:

libraries:
  - compony/global
  - compony/font--raleway--black-italic
  - compony/font--raleway--black
  - compony/font--raleway--bold-italic
  - compony/font--raleway--bold
  - compony/font--raleway--extra-bold-italic
  - compony/font--raleway--extra-bold
  - compony/font--raleway--etra-light-italic
  - compony/font--raleway--extra-light
  - compony/font--raleway--italic
  - compony/font--raleway--light-italic
  - compony/font--raleway--light
  - compony/font--raleway--medium-italic
  - compony/font--raleway--medium
  - compony/font--raleway--regular
  - compony/font--raleway--semi-bold-italic
  - compony/font--raleway--semi-bold
  - compony/font--raleway--thin-italic
  - compony/font--raleway--thin

(Only include the library definitions of the fonts that you need)

2) Use it in your CSS as follows:

font-family: 'raleway--black-italic';

All the fonts are named using the BEM-naming structure.