North is up and east is left. If you have trouble finding your target star, make sure you know the size of your instrument's field of view, and make a wire ring of that size using the degree scale on the edge of your chart. Slide the ring across the paper to preview what star patterns will cross your eyepiece. Be sure to turn the chart so north matches north in the eyepiece. One help in identifying R Leonis is its deep orange-red color.
Many comparison stars around R have their magnitudes printed on the maps above.
The magnitudes are traditionally given to the nearest tenth with the decimal point left out so that it won't be confused with a faint star. Once you've identified the variable, find a comparison star that looks just a little brighter than it and one that's just a little fainter. Look back and forth among the three and judge where the variable's brightness falls with the respect to the two comparisons as best you can. Suppose you decide R is two-thirds of the way in brightness from a star of magnitude 8.2 to another of magnitude 8.6. In other words it appears twice as far in brightness from magnitude 8.2 as it does from 8.6.