what is this interface for?

some.cs

internal interface IAppSettingsReader
{
    GasPeriodDto GetGasPeriodFromConfig();
    bool IsHourly();
    BalanceOverviewFilterDto GetFiltersFromConfig();
}

class AppSettingsReader : IAppSettingsReader
{
    public GasPeriodDto GetGasPeriodFromConfig()
    {
        int gasPeriod;
        int.TryParse(ConfigurationManager.AppSettings["GasPeriod"], out gasPeriod);
        return GasPeriodDto.All.First(p => p.Id == gasPeriod);
    }
}