In this chapter, Moses orders the people to set up memorial stones and instructs them to pronounce the blessings and curses of the covenant.
First, the people are briefly commanded to set up memorial stones when they cross into the promised land and write down the covenant upon those stones. This is conceptually similar to the two stone tablets of the covenant that Moses brought down from Mount Sinai, except that these memorial stones would be in the public and visible to anyone who passed by, while the two stone tablets were placed in the ark of the covenant in the most holy place in the tabernacle. If you place them in apposition, you can view the two tablets as being "God's copy" of the covenantal documents, while the memorial stones are "Israel's copy", since the first is placed before the LORD, while the second is placed before the nation (though only in one place and far from a lot of people). Note that in the book of Joshua we see the Israelites fulfill this commandment when they set up stones just as Moses commanded.
Next, Moses gives the people a framework for pronouncing blessings of obedience and curses of disobedience, which is another element of the Hittite suzerainty treaty. In this case, we see that 6 tribes are placed on each of two mountains where they would have antiphonally sung the words of the blessings and curses. The purpose of this ritual is to contrast the outcomes of these two paths, the path of life and the path of death.
What's peculiar is that after the blessings and curses are pronounced, then the Levites are instructed to answer with another set of curses. This appears to be distinct from the curses of Mount Ebal, which are listed in the next chapter. I'm not sure why there are two sets of curses, but one thing that I noticed is that the curses of Ebal are curses upon the nation of Israel, while the curses of this chapter are individual upon the people who violate the laws of the covenant. It certainly makes sense that the curses and blessings are for the nation as a whole, because the LORD is making this covenant with the people of Israel, so it is indeed a corporate treaty and not really individualized.
The curses in this chapter show that there is also a curse upon the individuals who break the laws of the covenant, even if the nation as a whole remains obedient.
With that said, most of the curses listed in verses 15-26 are repeating laws from earlier in the Pentateuch. Between two and four of them (depending on how you count) are from the ten commandments: You shall not make an idol, you shall honor your mother and father, then arguably v. 20 and 22 relate to adultery, while 24 and 25 could be related to murder and 17 could relate to coveting your neighbor's possessions or theft.
There are laws against having sex with animals and close relatives in Lev 20, and misleading the blind, distorting justice for the defenseless and accepting bribes violate the covenant's laws against injustice (which are vague and numerous, cf. Ex 22:21-23, Ex 23:1-9, Deut 16:18-20, etc).
These curses are therefore primarily restating the laws of the covenant, cursing those who break the commands, and then demanding that the people assent to it with "amen". "Amen" is a direct transliteration of the Hebrew, and it means "truly" or "truth".
Note that the repetition of Levitical curses and the word "amen" is another antiphonal section, just like the curses and blessings we will read in the next chapter. Antiphonal singing seems to have dropped off in popularity recently, but it is used heavily in choir music and was also used by the Israelites when these passages were originally written. I don't want to go into this as depth, but I just think it's interesting how for us, this part of Deuteronomy is a flat text, while for the ancient Israelites it would have been a song.