This page of the ear-trainer will test your skill at hearing diatonic intervals, the distance between two notes.
You are on the intervals (2 notes) page. This is the simplest section of the ear trainer. Intervals are only two notes, and it is definitely easier to recognize two notes than it is to recognize three or four note combinations. If ear-training is a new thing for you, then this is a good place to start.
If you are new to ear training, or just have questions about it, you should direct your questions to the IMusiK.ca Music Theory Chatbot. This artificial intelligence chatbot will be able to answer most of your questions. In fact, it was created specifically to work in conjunction with the IMusiK.ca Ear Trainer.
This free online ear trainer also has pages for Triads (3 notes) and 7th Chords (4 notes).
If you like the ear trainer, or have suggestions for new features, or just comments in general, please feel free to contact me.