A kilowatt-hour is the unit on your electricity bill. A kWh/24h figure tells you how many units the cabinet is expected to use in a day when tested at a stated ambient temperature, humidity and, for some standards, a pattern of door openings. Some labels give a yearly figure instead, which is simply the daily figure multiplied by 365.
Running cost is easy to estimate: multiply the daily kWh by 365, then by your commercial tariff per unit. Comparing two cabinets this way often shows that a slightly more expensive, efficient unit costs less over a few years of use. Remember that real consumption is usually higher than the test value in a hot, busy kitchen.
Compare like with like. Two figures are only comparable if they were measured to the same standard and conditions. A unit tested at a mild ambient will show a lower number than one tested at a higher ambient, even if it is less efficient in practice. Ask what conditions the figure refers to before deciding.