To give a basic answer to the first question--what is Marxism-Leninism-Maoism?--we can turn to the statement by Mao, put forward during the Great Proletarian Cultural Revolution in China: Marxism consists of thousands of truths, but these truths can be summarized in the statement: It is right to rebel against reactionaries.
Does this mean that all you need to know, in order to apply Marxism-Leninism-Maoism, is that it is right to rebel against reactionaries? No, it is also necessary to struggle to learn those "thousands of truths" that Mao speaks of, but that is an ongoing, lifelong process--everyone, no matter who they are and what their position is, must keep on learning these "thousands of truths" if they are going to continue to contribute to the cause of revolution. But at any given time and all the way through, their starting point and ending point--what they are guided by, in theory and in practice--must be that basic truth: It is right to rebel against reactionaries.
Turning to the second question--whose ideology is Marxism-Leninism-Maoism?--the answer to that can also be given in basic terms: It is the ideology of the proletariat--of the exploited class in capitalist society--and of no other class or group. Does this mean that people from other classes cannot take up Marxism-Leninism-Maoism, or that people from the proletariat can "automatically" grasp MLM as soon as they take it up? No, neither of these things is true.
People from other classes can and do take up MLM, but in order to really take it up, apply it and live by it, they have to consciously remold themselves--they must repudiate the stand and viewpoint of the bourgeoisie and petty bourgeoisie (the capitalist class and the middle class) and take up the stand and viewpoint of the proletariat, not just intellectually but in their hearts and in their lives. This is partly a matter of learning theory but it is above all a matter of practice and of struggle--of joining with masses in revolutionary struggle and of learning from the masses. This means learning especially from revolutionary proletarians, including in how they take up the struggle to grasp and apply revolutionary theory.
As for the proletarians, while Marxism-Leninism-Maoism is the ideology of their class, it is not something that comes "automatically" to them. It is not something that anyone, proletarians included, learns "spontaneously," especially living in a society divided into different classes, and above all a society dominated in every sphere, including the sphere of ideas, by the bourgeoisie. For proletarians to grasp and apply MLM is also a question of remolding themselves and a process of struggle. But this ideology is based on the position of the proletariat in society and it does bring together, on a higher level, the life experiences of the mass of proletarians. In turn, the position in society and life experiences of proletarians do provide the most solid basis for grasping and applying this ideology.
This ideology is not something "strange" to the proletariat. Just the opposite--Marxism-Leninism-Maoism concentrates the highest interests of the proletariat and represents the world outlook of the proletariat as a class with the mission to emancipate all humanity. As this ideology is taken up and wielded by masses of proletarians, it becomes the most powerful weapon for changing the face of the entire world.