You can install Audacity in a number of ways. The simplest process is to use the Ubuntu Software Center.
Open Ubuntu Software Center and do a search on Audacity:
Click on Audacity and follow the prompts to install Audacity.
To install Audacity via terminal. Open terminal via menu or via keys CLT+ALT+T.
When it opens, run command to add the PPA:
sudo add-apt-repository ppa:ubuntuhandbook1/audacity
Type user password (no asterisk feedback due to security reason) when it prompts and hit Enter to continue.
run following commands one by one to check updates and install audacity 2.4.1:
sudo apt update
sudo apt install audacity