Let's say the needle indicates LV=15.
Let's say you have a 100 ASA (ISO) film.
By rotating the dial, align the shutter speed you want to use with the mark of the ASA speed you are using.
For instance, align 125 (as in 1/125th of a second) with 100 ASA.
You will then immediately read, following the black, or white area, above the LV number indicated by the needle, the corresponding aperture for that ASA speed and that shutter speed, which should be f/16.
If you change the preferred shutter speed, e.g. 250, aligning it with 100 ASA, the corresponding aperture reading above LV 15 will be f/11. If you align 60 with 100 ASA, the f/value corresponding to the LV indicated by the needle (LV=15) will be f/22.

With practice you will soon find that the direct reading of LV is of more value than the explicit indication of a certain exposure "couple", and you will soon just read "LV=15" and in your mind you will know that, with 100 ISO, that means 125@f/16 = 250@f/8 = 500@f/5,6 etc.

Fabrizio