The calculator implements touch/click input through its keypad, providing these symbols to create formulas:
+ - ÷ / ( ). The = key will trigger evaluation of the formula. There is also a C key to clear all input, and a Del key to delete the last inputted character. There are two display fields: one shows the user's formula; the other displays the formula's evaluation.
The run this app locally, clone the project or download an archive. Then inside the project's root directory, run npm install, then npm start. You should be able to see it in a browser at localhost:3000.
This project was bootstrapped with Create React App. A lengthy guide to that generator can be found here.