In the Picture near the 3, we have Action and Create Task in the dropdown. How can I add more Actions in the drop down like "Create Note", "Log Call"

Below is my code:
public class StringArraytest 
{
    public static List<string> generateStringArray(integer n)
    {
        integer i=5;
        List<string> str= new List<string>();
        for(i=0;i<n;i++)
        {
            str.add('test '+i);
            system.debug(str[i]);
        }
        return str;
    }
}

Error: Challenge not yet complete... here's what's wrong:
Executing the 'generateStringArray' method failed. Either the method does not exist, is not static, or does not return the proper number of strings.