The circuit diagram for a capacitor shows two plates that are separated and not touching (like | |)

That's essentially what a capacitor is. It's an item that has two metal plates, separated by insulation (air, or some other kind of non-conductive material).

All you need to know is how it behaves.

• Capacitors like resistors, consume voltage.

However, in a DC circuit:

• The voltage that it consumes over time increases.
• This is because electric energy is becoming stored in the insulator (charging up).
• You can discharge the capacitor by connecting it against a resistor or appliance. It will dissipate all the stored energy.

This doesn't happen in an AC circuit, because as you know, the current goes back and forth. This causes it to charge up as much as it discharges, and hence it will stay at a net zero charge.

One consequence (feature) of this is that capacitors can be used as a decoupler. This means it can decouple AC waveforms from DC waveforms. It will block the DC voltage (as it's charging up the resistor), but the AC voltage can pass through with no problems.

Hope that helps!