I would like to know what namespace Sololearn does. if you ignore it the program works anyway.

Answer 1

Sure, this program works good anyway, because it is a simple program working alone. And there is show only a part of using the namespace SoloLearn
The next part, what about when you add this source file into another project, where is maybe from another coder another file with class Program too?
For this reason is used there a namespace keyword. In such big commom project a coder can write a namespace selector to determine from which scope is the class used.
From this (SoloLearn ), or another..

Answer 2

namespace it's mean group of
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

and if u don't using namespace and group of System.
the program it will not work