$$\require{cancel}$$
When current flows through a resistor, electricity is falling through a potential difference.  When a coulomb drops through a volt, it loses potential energy 1 joule.  This energy is dissipated as heat.  When a current of $$I$$ coulombs per second falls through a potential difference of $$V$$ volts, the rate of dissipation of energy is $$IV$$, which can also be written (by making use of Ohm’s law) $$I^2R \text{ or }V^2/R$$.
If two resistors are connected in series, the current is the same in each, and we see from the formula $$I^2R$$ that more heat is generated in the larger resistance.
If two resistors are connected in parallel, the potential difference is the same across each, and we see from the formula $$V^2/R$$ that more heat is generated in the smaller resistance.