Dear Pradeep Kumar,
Second week has one optional module. That you can go through it now. There are few optional modules in week 4 also. They will be available in 4th week.
Completion of a week's task is basically passing the quizzes with minimum 70 % and submitting the assignments & feedback, if any. There are group of links for each week. You have to go through each link.
All the best.
Dattakumar Chaskar