What is the difference between electronegativity and core charge? Please keep it simple and provide examples. From what I understand, electronegativity means that ANY electrons can be attracted, while core charge only refers to the valence electrons.

This is a great question, and you are on the right track because you realize that the difference is about context. Let me help clarify some of the details.
The short version is that core charge is something that we can calculate rather simply from the particles in an atom as long as we know how many valence and core electrons we have. It is a whole number. Electronegativity is found by experiment and, like most measured values, it is not a whole number. Many tables report electronegativity to two decimal places. Electronegativity is probably confusing because you potentially have not yet learned the context in which it applies. You will be expected to learn how electronegativity varies with position in the periodic table, and core charge can help you understand and remember this.
Core charge and how to find it
Core charge is defined as the charge of an atom’s nucleus minus the charge of the core electrons. I do not know how you were taught to find the number of core electrons. The easiest way I know is to take your element’s atomic number and subtract the number of valence electrons in a neutral atom. The valence electrons, as you probably know, are the s and p electrons in the atom‘s outermost shell, and they can be obtained by counting main-group (A group) elements across the row from left to right up to and including your element. When counting valence electrons, skip over the B group elements (the transition metals).
For example, consider magnesium (Mg). I have included a link to my favorite interactive periodic table, Ptable, so you can easily check the Periodic Table for all my examples. Magnesium has the atomic number 12. We know it has 12 protons, and neutral magnesium has 12 electrons. Magnesium is the second element from the left in its row, so it has two valence electrons. All of the rest of its electrons are core electrons, so it has 12 - 2 = 10 core electrons.
Now consider oxygen (O), on the right side of the table. Its atomic number is 8, so 8 electrons make up neutral oxygen. Counting from the left, we count two, then skip over the transition metals and count three, four, five, six valence electrons. Again, core electrons will be total electrons minus valence electrons or 8 - 6 = 2 core electrons.
Core charge is the atomic number Z (which is the charge on the nucleus) minus the number of core electrons. I think from your question that you understand that this represents the net charge that is attracting the valence electrons. Since we already subtracted valence electrons from atomic number to get the number of core electrons, when we take atomic number and subtract the number of core electrons, we get back the number of valence electrons in the neutral atom.
core charge = Z - (core electrons) but core electrons = Z - (valence electrons)
so
core charge = Z - (Z - (valence electrons))
= (valence electrons)
Remember here that core charge is always positive and is equal to the number of valence electrons in the neutral atom.
Core charge is useful for understanding periodic properties, especially atomic radius, since the increasing core charge going from left to right across the periodic table explains why the valence electrons are more strongly attracted and hence closer to the nucleus, making the radius smaller as you go from left to right.
Electronegativity explained
Now let us discuss electronegativity. The reason electronegativity is hard to understand at this point is that you are probably studying periodic trends and have not yet learned anything about the context in which it is used. Later, you will talk about the bonding that holds atoms together. All chemical bonding involves the attraction of positive and negative charges. One of the types of bonding involves two atom cores that are both attracted to the same pair of electrons. Both atoms are attracted to the electrons, and the electrons are attracted to both atoms. As a result, the whole thing holds together. This kind of bonding is called covalent bonding, with “co” suggesting sharing and “valent” indicating that it is valence electrons that are shared.
In covalent bonding, unless the two bonded atoms are the same element, they will pull unequally on the shared pair of electrons, so the shared electrons will be closer to one atom core than to the other. This affects the properties of the bond and the molecule that it is in. Electronegativity is the relative ability of atom cores of different elements to attract a shared pair of electrons in one of these bonds.
For now, you are probably expected to know that electronegativity involves an atom’s ability to attract electrons and how it varies with position in the periodic table. Electronegativity is greatest at the upper right (excluding noble gases, which do not usually form bonds). Fluorine is the most electronegative element. Oxygen, nitrogen, chlorine, and bromine are also highly electronegative.
Electronegativity is greatest at the right side of the periodic table because core charges are greatest in these elements. Electronegativity is also related to atomic radius. Remember, is it ultimately about the attraction of positive and negative charges, which depends both on how strong the charges are and on how close together they are. The elements with small atomic radii have their cores closer to a shared pair of electrons, so they are able to attract them more strongly.
All of the periodic properties are related, and you will understand and remember them better if you try to see the connections. Core charge affects atomic radius, and both core charge and atomic radius play a role in electronegativity (and in first ionization energy).
https://ptable.com/