The prompt is the computer saying "I am listening". Yours reads ada@computer:~$ — who you are, which machine, and where you are standing (~ is short for your home folder). You never type the prompt itself, only what comes after it, then press Enter.

echo prints whatever you give it, then moves to a new line. It is the terminal's way of saying something out loud, and it turns out to be one of the most useful commands there is: later on you will use it to build files and to make scripts talk to you.

The quotes keep the words together as one piece of text. Bash would print the words without them too, but quotes are a good habit: they protect spaces and punctuation from being treated as separate instructions.