[c#] Left function in c#

It sounds like you're asking about a function

string Left(string s, int left)

that will return the leftmost left characters of the string s. In that case you can just use String.Substring. You can write this as an extension method:

public static class StringExtensions
{
    public static string Left(this string value, int maxLength)
    {
        if (string.IsNullOrEmpty(value)) return value;
        maxLength = Math.Abs(maxLength);

        return ( value.Length <= maxLength 
               ? value 
               : value.Substring(0, maxLength)
               );
    }
}

and use it like so:

string left = s.Left(number);

For your specific example:

string s = fac.GetCachedValue("Auto Print Clinical Warnings").ToLower() + " ";
string left = s.Substring(0, 1);