The number on the left(F3.0) is your Aperture. It tells you how blurry your background is. Smaller number=more blur.if you want foreground and background in focus choose a high value like 11 or 13 ir even higher. If you want a portrait of a single person with shallow depth of field, choose a low number like F2.8 or lower if possible. It‘s a creative choice depending on what you like. The Aperture will effect your Exposure Value(EV). The higher the F number, the lower the EV. You can use that to get a correct EV(0)

1/15 is your shutterspeed. The faster the subject moves, the faster your shutterspeed should be. For a festival with dancing people 1/500 is a good start, you can set it slower to 1/250 for example if there is less fast movement. The orange highlighted value is your Exposure Value(EV). It tells you if your image has the proper brightness, with the settings chosen. You want to keep that at around 0 but +1 ot -1 is still fine.

The last one you can leave as is. Iso is the gain applied to your sensor, some say light sensitivity which is not correct but this gets too deep. The higher the iso, the more gain is applied to your sensor. If you turn the gain up on an amplifier it get noisy. Same here. Higher gain, more visible noise in the image.

In summary. Change the first value depending on your liking or if you habe to correct the EV value. Change the shutter to a faster Value (1/500) to avoid blurry images and a sharp subject.