so when you say celestial bodies are you referring to galaxies?
Galaxies, Clusters and Superclusters. Large objects.
if so then can it be possible that only the celestial bodies are moving around/in the universe and not that the universe is expanding?
The fact that they move away from eachother suggests expansion. Like chocolate chips in a baking cookie (better example than pancake mix.) Although this cannot be directly proven through observation, it is widely accepted.
and when you say the universe is thought to have borders in others words it's a hypothesis or has it been proven that there are borders?
This is difficult to understand. Keep in mind that space is not a perfect vacuum. There is a miniscule amount of matter scattered about. Consider an interstellar cloud. Each molecule in the universe has a gravitational and electromagnetic attraction to every other. The loosley packed particles collect tighter and tighter. After a core is formed, the outter material orbits the interior. Each orbit has a deterioration, in other words, it is slowly falling. This further compacts the interior. Picture a ball of play-doe. If you roll it inbetween your hands without changing the axis, it will be round, but flattened on the edges. Eventually, gravity wins the battle and all the matter comes together. The nuclear interactions cause the gases to ignite, giving birth to a star.
Galaxies work in the same way on a grander scale. As do clusters of galaxies, and superclusters, clusters of clusters. The universe is believed to work the same way, with outward limits. The scale is so large that it is hard to imagine.
if so then what is the universe expanding into?
The expanding universe is similar to a supernova. An exploding star can be seen as a small version of the big bang. The highly compacted matter results in an explosion which expells its contents to the surrounding area. The universe is thought so be expanding in this same way, that of an outward explosion.
and if our universe is expanding then we can assume that parallel universes (if they exist) are expanding also right?
If the universe in question still has inertia from the explosion that created it, then yes.
then would our universe eventually merge with pararllel ones?
A collision of two universes would hold unknown circumstances that we cannot fully account for. It is possible that universes are also moving away from each other. It may also be possible that a crash would create an immense explosion, or some kind of merge involving extra dimmensions.
haha i forgot about the whole mass can't be created or destroyed but what i find interesting is conciousness and what not and how the brain can send us to different realities and stuff like that and can make it seem so freaking real like dreams, certain drugs, meditation all that jazz...well since mass is recycled what happens to conciousness? or is conciousness and all that just a side-effect/anomaly of the universe/life?
Consciousness can be an exclusive trait to certain living beings. The fact that a dolphin can recognize its own reflection suggests some level of consciousness in, at the very least, the more intelligent animals. Honestly, no one knows if it will carry on after life.