To start contributing make your own branch such as feature/myblock starting from master.
Then add blocks to the collection by making a vue component files in the /components/<category> folder.
Styling is written in SCSS with BEM and mobile-first, so keep naming as clean and faithful to the methodology as possible. All the blocks style files can be found in in the /styles/blocks/<category> path, so when adding a new block add a new SCSS file here and remember to import it via main.scss.
Once you're done with your work, submit a pull request.