First make sure you have installed NodeJS,if not install it by downloading it from the following link
Download | Node.js
If you are on Windows, you need to install git ,install this from the following link:
You are downloading the latest ( 2.29.1) 32-bit version of Git for Windows. This is the most recent maintained build…
Open a terminal window, in my case I am using a mac, if you are on windows open command prompt and execute the following commands
git clone https://github.com/Uniswap/uniswap-interface
Once all 4 of these commands are executed successfully you should see a new tab opened with the locally hosted uniswap ui.