If you blow across an empty bottle, you can get the air inside that small chamber to resonate (make that booooooh sound). If you enlarge that small chamber to the size of your room, the air inside will still resonate (of course at different frequencies than the bottle).
The calculators you linked to show what the resonances (room modes) are for your room, based on the dimensions you enter. Easier to understand room modes if the calculator used a different style of graphics. Try downloading the Harman room mode calculator at the bottom of this page: https://www.harman.com/audio-innovations
For example, your 379 cm room length will result in modes/resonances at 46Hz, 91Hz, 137Hz, 182Hz, 228Hz, 273Hz, etc. The first 4 of these are mapped in the graph below, with each room mode colour coded so you can see where each of those problem frequencies are peaking or nulling.
Useful to view the modes this way because it can help you with placement. For example, the worst place to sit would at the midpoint of room length, because it's all loud peaks and quiet nulls (all extremes, no moderation). Frequency response would look like a roller coaster.
Notice that all the nulls fall at even divisions (half, quarters, sixths) of room length. You can avoid these by placing the listeners' ears at odd divisions (thirds, fifths) of room length. For example, at 2/3 back from the front wall, most of the problem frequencies are the same level. Good place for the listeners.
Understanding how to view these room mode graphs can help you pick seating location (and subwoofer/speaker locations) so that you get smoother frequency response (fewer/smaller peaks & dips). This will give the room correction system in your receiver a big head start. Best part: it's free (doesn't cost anything to move listeners, subwoofers & speakers).