Great question! Keep thinking big! Most people don't ask important questions like these.

The simple answer to your question is that the universe is made up of three things: 5% normal matter, 27% dark matter, and 68% dark energy. The not-so-simple answer to your question is...well, not so simple! So let's begin:

Normal matter is anything that has mass and takes up space by having volume. The stars in the sky, our planet Earth, and even you are made up of matter! To be specific, you are made up of around 7 x 10²⁷ atoms all vibrating with electrons, neutrons, and protons flying around inside of you! Despite the massive number of atoms that make up just you alone, normal matter only makes up a mere 5% of the stuff in our universe.

Dark matter is...not as simple to explain. Why? Well, honestly because not even the top scientists fully understand what it is. So they learn about it, by identifying what it isn't. Unlike normal matter (for example, you), dark matter neither reflects nor emits light...so how do we know it's there?

It began in the 1930s as astronomers were asking the same question that you asked "what is the universe made of?" In the process, they found that the galaxies in our universe are spinning very fast...too fast for them to be held together by the gravity from normal matter alone! Imagine that the galaxies are like people riding a merry-go-round that is spinning at 300 miles an hour. Even if they have good grips and strong arms...they should have been ripped from their seats by now! So there must be another force keeping them on this imaginary merry-go-round.

Thinking the same thing, in 1933 a Swiss astronomer named Fritz Zwicky suggested that the universe can't only be made of normal matter...it must contain..."DUN-DUN-DUNNNNN...DARK MATTER!" He called it dark matter because it does not reflect or emit light, but it most certainly is there. Today, all we know is that dark matter makes up about 27% of the universe, and that it is not like atoms...it's more like a medium or a substance.

Dark energy is the last thing on our list, but also the biggest. Dark energy makes up about 68% of our universe, and despite how much of it there is...we know so little about it! To grasp it, one proposed definition is that dark energy is the energy that comes from empty space in the universe. It's not necessarily a thing, but rather a property of space. Just like dark matter, it is not made up of particles and while we can't observe it directly, we know it exists because we have observed how it bends light coming from distant stars.

Hopefully this sheds some light on what the universe is made of!

This is actually a very interesting question. Though we already have a good amount of knowledge about our universe, there are still a lot of unanswered questions. I will talk about what we know so far.

To talk about what our universe is made of, I'd like to offer my answers in two directions. The general sense is that universe include all the space, time, energy, etc.

First, we can talk about our universe in a relative large scale, ignoring the details. In that sense, our universe includes galaxies, planets, stars, black holes, etc. There are also a large part of dark matter and dark energies which are less known to us. In this picture, our universe is filled with galaxies (includes planets, stars, etc.) in space, running with time, and don't forget the dark matter and dark energy.

Second, we can talk about our universe in terms of the basic particles, such as leptons (example electrons), hardons, and photons. Those basic particles will form the matter we know, from electrons, neutrons, protons, to atoms, to molecules, to compounds, and so on. Then it is more familiar to you now. Since those compounds and matter will form our Earth, the moon, our Sun, our solar system, etc. Here I want to emphasize again: those dark matter and dark energy are still little known. In this picture, our universe is made of those elementary particles and also include dark matter and dark energy.

The universe is everything, and so is made of everything.

About 60% of the energy in the universe is something called "dark energy" ("dark" meaning that we don't understand it and can't see it, not that it's evil or something like that). It seems to exert a repulsive gravity-like force that keeps the universe expanding.

36% of the energy is "dark matter" (same meaning of the word "dark"). This seems to be mysterious particles that have mass and gravity as we understand them, but don't interact with the rest of the universe except via their gravity (at least, not that we've ever seen).

The remaining 4% contains all of the atoms that we are familiar with. Of the atoms in the universe, about 90% are hydrogen, 9% are helium, 0.6% are oxygen, 0.3% are carbon, and everything else is in trace amounts.

Some of the universe is made up of the same atoms which make up the world around us. These atoms are listed in the periodic table, and they can be combined into the various molecules and compounds in everything we see, like dirt, tables, and each other. This "normal" matter only comprises about 5% of the universe though. Another 25% is said to be "dark matter", which we don't really know anything about except that it has gravitational effects, and "dark energy", which we also don't really know anything about.