A coil will come - or be hand made - in a given resistance. That value will not change (well, shouldn't, but some things will cause it to slowly drift).
Watts is a measure of power. Just like a 100 watt light bulb will give more light than a 60,
vaping at higher watts means more heat and more vapor.
Volts applied to a resistance will cause a certain amount of amps to flow, and that can be expressed as watts.
If your battery is fixed voltage, the only way you can change the watts is to put in a coil of a different resistance. The lower the resistance, the higher the watts.
If your battery is variable voltage, you can change the watts by simply adjusting the voltage.
Some batteries / mods are VW - variable wattage. They do the calculations for you and automatically adjust the volts to hit the user set number of watts, regardless of the coil resistance.
Some are VV - Variable Voltage. You adjust the volts directly.
Since manufactured
coils may or may not be exactly what they sold / labeled as, having at least VV is a good way to be able to tune your vape to suit your tastes. Some juices like higher watts, some lower. User preference is the rule, but in general, darker and "heavier" juices like higher watts, fruit and dessert juices lean toward lower watts.
Having an adjustable battery / mod is an easy way to get the result you want.