Eclipse throws errors. How to decide?

Question

Eclipse

Linux eclipse c++ throws errors. What do they mean and how to solve them?
Description Files Path Location Type
Symbol 'cout' could not be resolved first.cpp /hello line 5 Semantic Error
Description Files Path Location Type
Symbol 'std' could not be resolved first.cpp /hello line 2 Semantic Error

#include
using namespace std;
int main()
{
cout << "Each era has its own language\n";
return 0;
}