I wonder about spells that is described with a AoE(Area of Effect). If it's not a clear AoE spell like some attack stuff like Fire Ball etc. Do it have to effect everything within it's radius, or could I choose what to hit?

For example. The Light Spell Induce Calm(Level 40) affect everyone within 50 feet, couldn't I use it to just affect a single person, or myself? As long as the target is within its radius? Or could I change the effect radius or make the effect work in a cone in just one direction?

on page 115 under Common Spell Features: Target Selection.

"spellcasters will only affect the targets of their choice unless otherwise explicitly stated. On the other hand, they will not be able to de-select targets inside a radius unless they are perfectly aware of their existence."

so for Induce calm (listed in my book as banish negative emotions?), you could cast it for 'only yourself' but if there is a stealthy person following you that you do not know of, it would also affect them if they are inside the radius.

fireball as well as other attack like spells are generally under the "explicitly stated" case, and do not allow for target selection. Also, for defense against area attacks like fireball you must use block. If the attack is on the ENErgy AT and you cannot block energy, you take a -120 to defense.

as far as changing the affect radius, i do believe that is what the added effects are for, or for at least increasing the radius. As for decreasing it, i have always house ruled that you can make a non attack spell affect less of an area if you wish (you already pay for the entire area, so why not reduce the radius by 5ft if you want?) so making it into a cone or line for flavor doesn't seem to be too much of a problem. Just don't use it for munchkin reasons or your GM will be very mad

-EDIT- edited de-target to de-select target