What is the equivalent LTSpice diagram of the given varactor diode modulator (FM)
I realize most of this will fly over your level of understanding, but if you read about LC oscillators then come back to read this, it can make more sense.
First understand , how do Varicaps or “Varactor diodes”  work. Then read a few datasheets .
Then continue searching Wiki, on Tank circuits, Oscillators, RLC etc.
The RLC tank resonant properties may be computed for \$\omega_0=\sqrt{LC}^{-1}\$  and \$Q=\dfrac{R}{X_L(\omega_0)}\$ at resonance, while Xc of the varicap is in series with the fixed , Cf but lumped in parallel for a high impedance resonant circuit.  The ratio of Cv/Cf is tuned to give the maximum control range but not allowing a smaller fixed cap attenuate too much or contribute error. For now just consider the fixed cap to be bigger than this varicap. The two C’s are in series , yet shunt across L, so the net value is less, C=Cv*Cf/(Cv+Cf) , like parallel resistor calculation.
Consider all the tradeoffs and tolerances and a design margin budget for each part must be defined to satisfy all the design specs,  before you start choosing parts.
As the reverse bias on Varicap ( and all diodes ) increases the capacitance decreases logarithmically so increase the resonant frequency. Often the C ratio is defined from 0V (max Cj to 5V or max -ve voltage (12V). Varicaps just have tighter control on these tolerances than std. diodes. The maximum capacitance doesn’t affect the ratios but does increase with the size and power rating of any diode.  In Xtal tank circuits it has less pulling range but an XO with 50 ppm tolerance may be pulled &gt; 100 ppm with a varicap and it may take two in differential mode to get 200 ppm pulling range by reverse biasing each diode in opposite directions about the average of the range.
However for LC tank circuits there must also be temperature compensation as conductors for L have a negative or NTC coefficient of about -100 or more PPM/‘C change which requires precision ceramic caps with a positive tempco.  You may have heard of NP0 caps where this means the special ceramic has a nearly zero +/-50 PPM /‘C tempco. The last character was sounded like “oh” is actually a zero. Ceramic Caps also tend to have a negative tempco. but can be made to 0 (NP0) and some with N400 (-400 PPM/‘C), N200, N100 and P100. there are other values in this range, so it is the P100 ceramic caps that must be used to cancel the N100 or whatever characteristics of the inductor L.  Varicaps also have a tempco, making this a more complex solution to work over -40 to 85’C range. Yet it has been done, but obviously easier over a benign temperature range.
Then there is the matter of making the tank circuit do work in an oscillator with a buffer to some load such as an antenna.