No no you can either use the transformGeometry node an transform the input. Or use a pointMatrixMultiply node to transform your calculation point. Both accomplish same thing. However i dont know what your hierarchy is so i cant tell what to connect where.
should i start reading about matrices
Well ideally you should KNOW about them allready. In any case if you ever want to do anything even remotely 3d tech you should read about them. But to be honest theres nothing to it really. The matrix itself can be anything but the 4x4 affine transformation matrix in is simple conceptually. Its a mthematical entity A that is a linear combination in this case of 4 vectors , where each vector is 4 dimensions long. The 3 first represent the X,Y,Z unit vectors, the last their ofset from origin.
Math defines a number of vecor operations namely inverse, and multiply. Multiply results in the same as taking the subtransform and conevrt it to the parents space. The inverse makes the trasfrom backwards thus allows you to go in opposite direction. Further they define a point multiply where a point is multiplied by a matrix. this accomplises moving the point form local space to whatever global the matrix defines. Thats about all you need to know.
