Hi Sonia. Thats a very big question in a few words I think. As ever how you see this depends on view. Here's one:
This world is inherently a dog eat dog and impermanent environment, and in that situation there's inherently suffering involved in life/survival. (if nothing else there's aging, illness, climate, natural threats, the need to eat other living things and so on)
That said selfish and egotistical behaviours account (along with our typical ignorance of how to live wisely) for much of the suffering we experience - living with wisdom and compassion (through love) can eliminate much of this. Buddhism is clear that this is important in giving us the space required to see that there is a path to escape. (one by which it can be transcended)
Both Buddhism and ACIM teach that in the end we must stop reacting aggressively to what life and others seem to do to us - ACIM uses the term forgiveness, Buddhism talks about caring but not caring - equanimity. Both because by not doing so (by lashing out even if only mentally) we in effect make real the world and its nastiness in our minds. At the physical level our actions in lashing out make the reality we each experience.
This seems a lot more logical if we can accept that both what we take as ourself (our body and conscious mind) and the world are actually creations of our own mind and ultimately unreal - we project as apparently external that which we fear and dislike, so that when we lash out at it we're in effect attacking ourselves. (this is also the reason why universally loving behaviours towards all are the only way - we're in effect loving ourselves)
This however is only a part of what we're about, there's no heaven possible in this reality.
Escape from this reality requires that we awaken from the dream, that we cease to be taken in by its appearance of reality. It's in fact the work of ego, which out of fear wants us to remain separate from God/higher mind. To achieve this we must stop the above lashing out, as this gives it reality in our minds. At the physical level it creates suffering for all, and drives us deeper into the dream.
Hence the need for the forgiveness ACIM talks of - 'it never happened'.
The eventual transcendence of this reality makes possible our return to God, Heaven, the reality where all is joy and love or whatever you call it.
Getting there is another matter, and no small task. It's in fact the work of many, many lifetimes. We have to transition from unconsciously digging ourselves deeper into the dream, to deciding there must be another way, to starting to see intellectually that love is the way, to learning what this means in practice, to using willpower to try it out and gain experience, to eventually in a wise, compassionate and skillful way deploy love as our natural unthinking response, to eventually it's becoming the only response we're capable of.
At which time we wake up, and with the dropping of our belief in this reality it falls away.
All 100% in opposition to our conditioning and the prompting of society and our instincts.
No easy task. We all get there in the end it seems, but it's not the work of an evening, and it extends far beyond simple intellectual understanding (which counts for little). We become something else (or we rediscover what we truly are and always have been) - something far greater than a frail physical body and mind in a hostile world.
The most effective means of speeding the process up seems to be self work - with the assistance of Grace/higher mind, and while following one of the spiritual paths.
Sorry not to provide a simpler answer Sonia, or to respond directly to your questions. The good news is that your seeking spiritually suggests that you are probably well on the way - it's said that it's with conscious enquiry that our progress really accelerates.
Maybe you'd consider (if you are not already) working one of the spiritual paths - it's only over time that this stuff starts to become real....