I am currently writing 1st episode of my story but i am a bit confused that how many lines 1st episode should contain.
It depends on your directing, really. Advanced directing often consists of more code and therefor have more lines.
Instead of lines, try to go on time. How long does it take to read through the episode? The prefered lenght for most readers tend to be 15-20 min. 10 being to short to “waste” a pass and 30 to long/losing interest. Of cource it also depends on what the episode contains, how intriguing it is.
Happy to help.
Good luck with your story.