Don't go on this alone, but here you are:
Atoms contain protons and neutrons (nucleons). These are found in the nucleus. Electrons are (for GCSE) arranged in energy shells (circular orbits around the nucleus).
The periodic table is arranged in order of atomic number (the number of protons in an atom). In a stable atom, there is an equal number of protons and electrons. This means that elements in a group on the periodic table (vertical column) share similar properties, as they have the same number of outer, bonding electrons.
Very important: an atom is happy, if you like, when it has a full outer shell of electrons. First shell: 2. 2nd,3rd,etc: 8
Bonding:
Read up on covalent, ionic, and metallic bonding. Here's a brief summary.
Covalent bonding occurs between two non-metals (mainly right side of the periodic table). The bond is formed when two or more atoms 'share' electrons to become stable (complete both outer shells). Examples: O2, CO2. (Not all bonds are clear cut covalent or ionic, some may be in-between)
Ionic bonding is usually between a metal an a non-metal. The metal donates one or more electron(s) to one or more non-metal(s), becoming a cation (positive ion). It is oxidised - it now has a full outer shell because it has dropped down to the next energy level. The non-metal gains an electron to become an anion (negative ion) with a full outer shell. The 'electrostatic force' between the opposite charges, + and -, forms a strong bond. Eg. NaCl
Metallic bonding: metals give up their outer (valence) electrons. They become cations in a 'sea' of delocalised (not delocalized; I'm English) electrons. The electrostatic force forms bond - stable structure. Eg. Fe
Whether an atom loses or gains an electron depends on which requires the least energy, eg: Sodium has one electron in its outer shell - it is easier to lose one electron than to gain seven! Chlorine has seven electrons in its outer shell - gaining one from the sodium makes the outer shell complete. This is an ionic bond.