They are different tenses. It means "I want to". Here are some examples: "I am meant to be studying now but I am watching TV instead." "I meant to buy bread earlier but I forgot to." "I mean to visit you more often but I am very busy." "I have been meaning to phone my friend but I can't find his number."

If you 'mean to do' something you intend to do it. It's often used in the past, to refer to something you had wanted or planned to do, but for some reason you didn't do it. 'Mean doing something'?? I'm not sure that form exists. Maybe I'm just not a very good Guru....