what's difference between interface.method() and method()

Question

I've got 1 solution contains 2 project - 1 console app, 1 class library. Class library: Istep.cs

interface Istep
{
    bool Excute();
}

Sample.cs

bool Istep.Excute()
{
   // do something
}

Console app - program.cs

Sample sample=new Sample();
sample.           // this can't found Excute method

if i change Sample.cs as following:

Public bool Excute()

sample can find excute method .

public class Sample : Istep

after i changed Excute without full qualified function name, right click Istep, click implement interface, VS will genarate a new excute method with full qualified name. so that's my question.

Thanks in advance!