Just to remind us, the first time the term m'lacha is used in the Torah is here:
Shmot 35:(2) Your m'lacha will be done for six days and on the seventh it will be holy to you, a shabbat shabbaton to God; anyone doing m'lacha on it will die.
When we read this verse now, we understand that the activity which is prohibited on Shabbat, m'lacha, is the same sort of activity which created the universe and the same sort of activity used to build the mishcan.
Chazal had a tradition that there were 39 m'lachot used to build the mishcan. They are listed in the Mishnah Shabbat 7:2. I won't go into them all now but we'll touch on some or more before the end of the week.
So, when the Torah prohibits m'lacha on Shabbat it is reasonable to think that it is prohibiting the activities which were used to construct the mishcan. Again, these are all creative acts which have a specific purpose and must be carried out with specific intent as that was our conclusion about the meaning of the word m'lacha in our last post.
What is particularly interesting to me is that we might also understand that the building of the mishcan is/was truly parallel to the creation of the universe. We pointed out how strikingly similar the language describing each is. If that is the case, it would be reasonable to think that the m'lachot used to build the mishcan are all in some way very basic elements of construction--but not just construction of a building, but construction of a microcosm of the universe. Tomorrow we'll look broadly at the list of m'lachot to see how we might understand all that better.
We could also turn that around and say that the universe is in some cosmic way a mishcan, a dwelling place for the Divine presence. This idea is already promoted in several places in the Tanach, i.e. that the entire universe is God's dwelling place. It was fitting when God wanted to focus His/Her Presence in this world that He/She chose to do so in a structure and with a series of activities which were the human analog to God's activities which created the universe.
Thus, when we refrain from doing those m'lachot on Shabbat we are, in our little way, completing the Creation just as God completed the Creation by ceasing m'lacha on the seventh day.
So, Sophie, not a full answer but we're getting there :)