If you want to make the window bigger, click on the bottom right corner and drag it outwards. Bash stands for 'Bourne again shell.' There are a number of different shells that can run Unix commands, and on the Mac, Bash is the one used by Terminal. In the title bar are your username, the word 'bash,' and the window's dimensions in pixels. You’ll see a small window with a white background open on your desktop. To open it, either open your Applications folder, then open Utilities and double-click on Terminal, or press Command-space to launch Spotlight and type 'Terminal,' then double-click the search result.
The Terminal app is in the Utilities folder in Applications. Curated Mac apps that keep your Mac’s performance under control.