In this animation, you'll see an example of a redox reaction between the atom magnesium (Mg) and the molecule chlorid (Cl₂)

To understand what is happening in the example above, you'll first need to understand what a redox reaction is:
A redox reaction is a chemical reaction, happening when 2 metals either give their electrons to another atom, or molecule, or get electrons from another atom, or molecule.
This process is called oxidation or reduction. An oxidation is the loss of electrons and a reduction is the receiving of electrons.
When losing electrons, a atom or molecule, will either be positive charged or negative charge, depending on oxidation and reduction process.
When a redox reaktion will take place, all electrons from the outermost shell, will be given to the receiving atom, or molecule, which should them mean, that both should now satisfy the octet-rule, where all atoms, or molecules, who participate in a redox reduction, should have a electrons in their outermost shell

The animation shows magnesium losing it's 2 electrons, in its outermost shell, to the molecule, chlorid.
Both will now have eight electrons in it's outermost shell.