The impedance of a resistor is R
The complex impedance of a capacitor is $$\frac{-j}{w \cdot C}$$
The complex impedance of an inductor is $$j \cdot w \cdot L$$
What you need, is to work out the impedance using your understanding of series and parallel connected components, substituting these impedance expressions. You will end up with the j terms which are complex numbers. It'll end up looking like:
$$\frac{\left( \frac{R \cdot \frac{-j}{w \cdot C_2}}{R+\frac{-j}{w \cdot C_2}} +( j \cdot w \cdot L)\right) \cdot \frac{-j}{w \cdot C_1}}{\frac{R \cdot \frac{-j}{w \cdot C_2}}{R+\frac{-j}{w \cdot C_2}} +( j \cdot w \cdot L)+\frac{-j}{w \cdot C_1}}$$
Expand the mathematic equation, multiply by the complex conjugate and take the square root. The complex expression z $$\frac{a+b\cdot j}{c - d\cdot j }$$
Has the conjugate z^* $$\frac{a-b\cdot j}{c + d\cdot j }$$
You flip the polarity of the j expressions from positive to negative or vice versa
Multiplying the two $$z \cdot z^*=\frac{a+b\cdot j}{c - d\cdot j }\cdot \frac{a-b\cdot j}{c + d\cdot j }$$ Yeilds a real expression (not complex), but it is the square of the real magnitude, so you square root the answer