In order to use resonant, you have to generate it first. This page lists the different machines used to create and store resonant crystals.
To create resonant crystals you will need a generator and something to store it in, generators create 'pulses' that charge storage devices at a fixed rate. Connect the output of a generator to the input of a battery/capacitor with resonant cables and it will gain a set amount of resonant per pulse. Each machine has pulse information listed.
While you can store resonant crystals in normal chests/barrels like you would ordinary items, you have to use special storage devices in order to power crafts and collect the crystals.
You can also use the resonant crystals stored in storage devices to power resonant machines, activating the dropper on a battery/capacitor will generate resonant pulses and drain the stored crystals.
A battery: 2 composite blocks and a dropper
Batteries are the more efficient, but more expensive way to store resonant, the dropper is used as the input and storage.
Capacitor: 2 iron blocks and a dropper
Capacitors are a cheaper but less efficient storage method, the dropper is used as the input and the barrel is the storage.
Generators are how you actually generate resonant crystals. (go figure) Connect a generator to a storage device, activate it, and you will start producing resonant.
Side view + power flow
Front view - note the direction of the furnace
Combustion generators get their power from burning fuel, to build one just place a redstone lamp on top of a blast furnace and activate it, direct resonant cables out of the back of the furnace and place the fuel where it usually goes.
Power flow - the dropper is facing into the cable
Once built solar panels require no maintenance and will generate pulses on their own, (magic!) the only requirements are that they must have sky above them and they must be above sea level. (y63)
Wind turbines are similar to solar panels, once activated they passively generate pulses. But unlike solar panels the frequency is determined by height, rather than time of day.
View from above
Hydropower generators (aka water turbines) create pulses from flowing water blocks, they are very reliable but expensive.
View from above
Geothermal generators are similar to hydropower generators, they are reliable and produce tons of power but are expensive to construct, requiring difficult-to-obtain blocks such as obsidian and netherbricks