In first instance, I only experience my consciousness. This observes coherent experiences that make me believe in an outside world: if I see water, the believe that there is something - water - that feels in a certain way and tastes a certain way and still exists in a later time unless I drink it - is the much simpler explanation of the world than all these water related experiences being independently produced in my mind without an outside world.
From these coherent experiences we start to model the world around us, each with their own mind and world model and believes about what is true. There are facts about which one can say that they are (probably) true: if they are coherent to all observations accessible to us. Facts in this category fall into the category of objective reality. Some of these facts are part of almost every minds world model - like gravity existing - and some are not obvious enough to be part of every minds world model.
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There are also ideas which are in principle not verifiable. For example: (1) we live in the matrix or (2) there is a parallel universe which does not interact with ours at all and there is a goldfish. What do these sentences mean? 1: Provided the matrix is running, our reality is exactly as one would describe it without the matrix existing. In that sense, it doesn't matter whether the matrix exists or not. But it can be that the matrix is switched off. Then an interaction with our perceptible world occurs. If this state of affairs is true, it is not verifiable, but other future observable events are than if the fact is not true. In the sense one cannot judge whether it is true, but the truth content can be assigned some meaning for the reality. But as long as there is no disturbance of the matrix or an interaction with the observable world, there is no difference at all within the observable world between the two scenarios that the fact is true or not true. In the case of the 2nd fact it is different: it is and will never make an observable difference whether it is true or not, and the notion of truth is meaningless.