Why is code sometimes read from left to right and then others from right to left?

using System;
namespace Treehouse.FitnessFrog
{
    class Program
    {
        static void Main()
        {
            int runningTotal = 0; /*read left to right: we're making an int variable called runningTotal and assigning it the value 0 */
            Console.Write("Enter how many minutes you exercised: "); //read left to right
            string entry = Console.ReadLine();        //read left to right
            int minutes = int.Parse(entry);  //read RIGHT side of the equals sign to LEFT?  
            runningTotal = runningTotal + minutes; //read the RIGHT side of the equals sign to LEFT for reasons unclear to me
            Console.WriteLine("You've entered " + runningTotal + " minutes."); //read left to right
        }
    }
}