The rules
Capacitors work the opposite way to resistors. In parallel, their values simply add, and so do their current ratings. In series, the total is less than the smallest: 1 ÷ C = 1 ÷ C₁ + 1 ÷ C₂ + …, and the voltage ratings add up, which is why capacitors are sometimes put in series for high-voltage use, with balancing resistors across each. Inductors follow the same rules as resistors, as long as their magnetic fields don't couple: in series they add, and in parallel the total is less than the smallest.
Making odd values
A tuned circuit often needs a value that isn't made, such as 68 pF plus a little. A small fixed capacitor in parallel with a trimmer is the usual answer. For inductors, keep combined coils apart or at right angles so their fields don't interact, or simply wind the value you need with the coil calculator. The LC resonance calculator tells you what value you need.
Questions
What happens to capacitance in series?
It goes down. Two equal capacitors in series give half the value of one.
What happens to capacitance in parallel?
The values add up.
Do inductors add in series?
Yes, if their magnetic fields don't couple. In parallel the total is less than the smallest.
Why put capacitors in series?
To get a lower value or a higher voltage rating. Use equalising resistors across each one for high voltages.