In a super small nutshell, these chapters have one event:
Moses and the Israelite builder get to constructing the Tabernacle to the exact specs that God gave them in Chapters 25-31. God comes down to hang out in it, and the Israelites move whenever God's cloud of fire leaves the tent. "But if the cloud was not taken up, then they did not set out until the day that it was taken up" (40:37). That's it. That's the end of Exodus.
The literary structure of this section is almost exactly the same as all the regulations for the Tabernacle in Exodus 25-31. So, in 25-31, if God said, "Bob, you should go over there, and build a box, and this box should be 2.5x1.5x1.5 cubits," then Exodus 35-40 says it this way: "Bob went over there, built a box, and the box was 2.5x1.5x1.5 cubits."
Since the text here is the same, check out our analysis of "Chapters 25-31" to understand why the text uses this kind of language.
But let's consider a larger question. In Genesis, the writers spent a few chapters trying to sum up the creation of the universe. In Exodus, the writers spend about five times as much space on the Tabernacle specs—down to the last cubit. Why is this? Why repeat this kind of text?
For starters, we have to remember that whoever was writing this text had a huge interest in the Tabernacle. Biblical writers don't repeat unimportant things, so the specs are really important. If you needed to include blueprints for your club's headquarters and info on the club's origins in the same document, what would you spend more time on? Probably the blueprints: they mean continuity for everything else; and if that building isn't built perfectly, the rest won't get preserved.
People also speculate that this section of Exodus was written by a source within the priesthood. Remember, the forerunners of the priests—Aaron—screwed up big time with the golden calf. Could all of these repetitions be trying to make up for that? Maybe the writer wanted to focus the reader's attention on the priests' new source of power rather than their old source of disgrace.
One final note about the end of Exodus. Then we're done, we promise.
God had said before that he wasn't going with the Israelites into Canaan. Remember? In 33:3, he said he was done with them: "I will not go up among you, or I would consume you on the way, for you are a stiff-necked people."
But by the time we get to the end of Chapter 40, the spirit of God is hanging out in the Tabernacle. Explanations? It could be just an angel. Or God could have meant that he would go with the Israelites to Canaan but not into it.
When it comes down to it, the Biblical presence of God is its own thing entirely, and no one seems to be able to figure it out.