Hello Ruchith Bm,
Integration is summing up elements of same type(like dx,dA,dV) over an interval like area ,volume,surface.for integration to be valid the interval chosen should be such that the function which we are integrating(the function containing the x element say) should be continuos in that interval
The best way to understand integration and differentiation is by closely analysing their application in physics like find the net electric field at a point by a group of charge since we can cannot individually add the field of each charge ,we use functions to ease the task
Differentiation on the other hand is the opposite process where we divide a function's changing variable say x into its smallest segment
Watch videos and read more about the subject on internet if you are more interested about the topics because one cannot literally make you understand about these subjects by small write ups such as this
Also there is not much need to understand the theory behind these as far as 11th 12th curriculum is concerned.You will only need to know how to integrate and differentaite for these level of education