Q:

What does "name::name" means in C++?

I would like someone to explain me the "name::name" syntax and how it is used on C++ programming. I have been looking through but I don't get it yet. Thanks for help.
Here is context code:
void UsbProSender::SendMessageHeader(byte label, int size) const {
    Serial.write(0x7E);
    Serial.write(label);
    Serial.write(size);
    Serial.write(size >> 8);
}

A:

:: is the scope resolution operator.
std::cout is the name cout in the namespace std.
std::vector::push_back is the push_back method of std::vector.
In your code example:
void UsbProSender::SendMessageHeader(byte label, int size) const {
    Serial.write(0x7E);
    Serial.write(label);
    Serial.write(size);
    Serial.write(size >> 8);
}

UsbProSender::SendMessageHeader is providing the definition for the SendMessageHeader method of the UsbProSender class.
Another (more complete) example:
class Bar {
    int foo(int i); // forward declaration
};

// the definition
int Bar::foo(int i) {
    return i;
}

