I am 16 at the moment. I am really interested in physics. Especially particle physics. Can someone please tell me how to start learning the subject. like what to learn first. like which fundamental theories and concepts, the math needed in it, etc, etc.
What you want to learn is called "Quantum Field Theory", but it is a subject that requires having learnt other things first. At least some differential calculus, Special Relativity and Quantum Mechanics (a subject that itself requires some other previous knowledge).
But you can try. The simplest serious text above popular level may be "Quantum Field Theory Demystified" by David McMahon. It is a nice, cheap book, with short chapters, good explanations, solved examples and a quiz at the end of each chapter. This can be the starting point. (Later edit: Warning! It has many errata and notational inconsistencies, although the general explanations and complexity level is still nice... There seems to be no alternative text at this introductory level, although I am finding Srednicki really useful and clear - but that is a big book departing from a somewhat higher level of knowledge)
With respect to McMahon's books, please see the cooperative effort to make errata sheets here