What really is Spacetime? What is a good definition on Space, Time and the most specific topic "Spacetime"? Because someone told me that spacetime is the foundation of the entire universe?
And also, Is it possible to create spacetime?
 A: The notion of dimension is related to the idea of distance. To say that time is like another dimension typically implies that we can measure some sort of "spacetime distance" between two events separated by space and time. Let's see how this is different from the old picture of space and time. 
In the Galilean/Euclidean/Newtonian picture, we live in a universe with three dimensions, and the distance $\Delta s = \sqrt{\Delta x^2+\Delta y^2+\Delta z^2}.$ This quantity is invariant under rotations of the coordinate system or shifts $x\rightarrow x+\epsilon$. Notice that the separation between two events separated not only by a distance but a time cannot be captured by a single number.
In special relativity, time is like the another dimension. We have an invariant "spacetime distance" $\Delta s = \sqrt{\Delta x^2+\Delta y^2+\Delta z^2 - \Delta t^2},$ which is invariant under spatial rotations, shifts, and also boosts. In other words, two observers traveling at different speeds will agree on the "spacetime distance" between two events. This is not true in the Galilean picture. 
A: Position and time are the parameters by means of which we identify where and when an event happens. Space is the collection of all possible positions, and spacetime the collection of all possible (time,position) pairs. Spacetime can therefore not be created by processes within our universe, it is the movie-like arena where everything happens.
Empirically, one finds that spacetime can be described mathematically by the structure of a 4-dimensional Lorentzian manifold without boundary. This is why we have 3 position coordinates and one time coordinate, no matter how we set up the coordinate system.
