How do you write a script with three stories?

Find a theme that matters to you - loneliness, friendship, hobby, rising cost of fuel, changes in diets - whatever it is that pushes your buttons, so to speak. Then note down as much as you can about the chosen topic/s. Let it flow, so you just let your subconscious mind 'unload' and get everything down. Go through it and begin to tie together commonalities, using the great storytelling device, "What If?"

Find common themes and resolve them.

I suspect you write three short scripts that somehow make sense when performed together as a set. If I were doing this, it would be a play in three acts.

Maybe it's the same characters at different stages of their lives. Or maybe it's the same setting, new characters and different approaches to the same issues. Or maybe it's a single clear theme or situation and how three circumstances play out.