Actually two questions maybe 3

1 what does heaven mean in Islam. What will it look like. What will it be like, who will be there, when will people go There? Are there any mid-point between life here on earth and Heaven (ie purgatory or rebirth into another life on earth. Is heaven Eternal. What will you do there?
2 (this is to me the more important question.) How does a Muslim person know they will go to heaven when they die. In Islam how does God (Allah) determine who goes to heaven. And who does Not.
Once a person in their earthly life has been given entrance to heaven when they die, can they lose that, and if so how?
If a person. Loses their right to go to heaven can they regain it, and if so, how?
To Muslim people reading this. Do you know right now if you are going to heaven or Not. And why/how do you know this?
Thanks And anyone replying is welcome to say they if they want to ask the same of me, and I will answer, based on my own actual experiences.