Component 1
# following https://www.polymer-project.org/3.0/start/first-element/intro
npm install npm@latest -g
npm install -g polymer-cli@next
cd component-1
polymer serve --open
for styling the component through the project, see https://www.polymer-project.org/3.0/start/first-element/step-5#extra
App 1
# following https://www.polymer-project.org/3.0/start/toolbox/set-up
polymer init #select: polymer 3 starter kit
polymer serve
# in step 3
npm install @polymer/paper-checkbox@next --save