There will be spoilers if you keep reading
Firstly, he is shown surviving inside black holes. From where did he got oxygen? Perhaps from oxygen bottles. But, in an intense gravitational pull, how he survives? He would have got torn apart! am I right?
The popular press says the word black hole and it is a bit vague what they mean because there are some different parts that fit together. There is an event horizon and that is right on the boundary between the outside and the inside. And there is a singularity and it is on the inside. And there are tidal forces and they are in between the event horizon and the singularity and even outside the horizon as well.
The tidal forces are real, and we know that because they are outside. But they are weaker near the boundary when the black hole is larger. In the movie the black hole is super large. So the tidal forces are real but out there near the boundary they are super small so they don't hurt or do much of anything. You aren't ripped apart standing on the surface of the earth and a big enough black hole can have weaker tidal forces than the earth makes. Weaker near the boundary that is.
Or is it really possible to survive inside black holes with enough oxygen available?
So a super big black hole doesn't hurt you when you are near the boundary. But the thing about the event horizon is that you can't see the inside from the outside. It is similar to a river where the water is flowing at the speed of sound. In such a situation you can't hear sounds from downstream. If there was a point where the river narrowed enough to reach that speed then you would never hear from things that crossed it (without going and crossing it yourself to go hear it). We (people outside) can't get any information from the inside.
Spoiler: In fact in the movie that is the whole point. They wanted to get information that was inside and you can't get that from the outside the only way to get information from the inside is to go inside.
Can one really travel back the time inside black holes?
There is no good reason to think you can. And in fact, if you could go back in time and get outside then you can get outside. Which defeats the whole definition of the event horizon as a boundary between the inside and the outside where things can't cross from inside to outside.
That said: We don't know what happens inside exactly because we can't get information from the inside to the outside. Which means the other parts of the black hole such as the singularity are just hypothetical. Every single thing inside is hypothetical.
That is, is time as a dimension really possible?
That's normal to consider time as a dimension. You do that so that you can talk about how measurement of lengths of curves in 4d depend on your path in 4d not just on the endpoints in 4d. And clocks for instance measure lengths of curves in 4d and we need to explain how two different clocks that start and stop at the same place and time end up having ticked different numbers of times if they take different paths.
And they can do that even if each just felt like it was floating weightlessly in a vacuum the whole time (for experts the clocks can take different geodesics around a rotating body, geodesics that start and stop on the same events, yes that is possible to have multiple geodesics between the same events uniqueness is only for arbitrarily small regions).
If yes then how?
How do you show time is part of a 4d spacetime? You can theorize it and make models to get predictions and see if your predictions work out. But that becomes hard if there is time travel. In general a prediction is an if-then, if the situation is like this, then this other thing happens. It's not clear what predictions you would or could make with time travel.
Then, he is shown that he is alive though he falls into black hole.
Crossing the event horizon might be perfectly safe if the black hole is super big. Everything else is pure speculation.
Does this mean, that with the help of appropriate technologies in future we can really escape black holes?
How would we know? What if you go in and then when you go out you find a world that reminds you of your own world but is actually different? I just asked a question about that a couple of days ago. Because I wanted to know the criteria people use to distinguish whether it is your world or just looks the same.
It is possible that the people that see you go in never see you come out and never see you go back in time. And it is possible that you go to a world that looks like your world in the past but is actually a different world.
In Bermuda Triangles, rumours are there, that one can see the past. So, is it just like a minor black hole with immense gravitational pull, that we can travel past like the actor did in the cinema?
That's makes no sense. A medium sized black hole would destroy you before you even got close to the boundary. A small one would just eat part of you. And a big one isn't going to fit and the whole planet would notice if there was one there. Bermuda is not related to any physics, there isn't room for a black hole that could do anything. And even so, you wouldn't be able to see things with a black hole, black holes hide things, hence they are mysterious because we don't know what they are hiding.
But seeing the past is normal. When you look in a mirror you see the past, even if only a nanosecond for every half foot you are in front of the mirror. You don't need anything spooky to see the past. Now affecting the past is completely different. That means for instance they see the future. How can you make predictions if you've already seen the future?
Does immense gravitational pull affects time?
It's not the pull. But time does flow differently in different regions.