Also, I have a query of how one can define spells?.
Example: Air Bomb, would I need to touch or point to the target; where would i create it and at how much distance!.
All spells are line of sight targeted until/unless you get to the really high powered spells. I don't think you need to point even, so long as you hold the target firmly in mind.
Can you also case multiple spells per round!
Depends on the situation. There are not set "rounds", but if you're casting a spell that another player might want to do something about (say, fighting a magic duel with another PC) then you basically need to just do one at a time. If you're standing on a hilltop as a bunch of pikemen charge at you, you may only have time to cast one spell. If, however, you are flying through the air above bow-shot range, you can probably cast as many spells as you want to roast the army below
Can you interconnect spells and wait for interactivity! Can/how_can one do it?.
lets say I want to throw a stick in random direction with an air bomb, but for that I would need to cast Summon Stick, throw it infront of me and I want to cast Air bomb immediately. But I won't be able to do it from RP perceptive because it would be a RP fail/mechanic-ism fail if I were to fizzle casting summon stick and then write it up that I threw it infront of me)
Spells don't fizzle. Spontaneous casting can fizzle, but spells are not the same. They either work, or they don't (because you don't have enough concentration, energy, or skill), and you know which it will be.
Magic also can't have direct interactions with other magic, as that would require a base of Magic, which does not exist. However, the example you described would be fine, as you're modifying something physical and then modifying something else physical, and those can interact with each other. Similarly, you could create an oil slick, and then light it on fire.
