Answer:
I am a portal to another world which you cannot enter. Only you can see me but I can't see you.
What is the word that even in plain sight remains hidden?
Where did the baseball keep its lemonade?
I belong to you but others use me more often than you do
What is always coming but never arrives?
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.