UI-wise I second the recommendation of starting with an existing component library. Bootstrap is still a good start.
UX-wise - which would be the process of determining the process, I recommend taking a look at the “breadboarding” approach as described here.
https://basecamp.com/shapeup/1.3-chapter-04
For this, all you need is pen and paper. The process is low fidelity, cheap, and lets you quickly flesh out your ideas toward concrete screens at which point you can reach out for the component library.