Main mean "I" and Maine mean also "I". But if we do any activity in present that we shall use the word "Main" and if we did any activity in past form than there we will use " Maine". So if you say " Main thik hoon" it is correct, but if you say " Maine thik hoon" it will be wrong. If you say "Maine lunch kiya" or "Maine lunch kar liya" both are right sentence, but if say that "main luch kiya" it will be wrong. If you use these words in daily life than it can be easy to understand difference between Main and Maine

"ne" is the particle.one who do something is called subject(in hindi--" karta ". you should remember this like a --- karta-ne, karm- ko, karan- se etc. jis tarah subject ke saath "ne" particle hota hai, usi tarah object ke saath "ko" particle hota hai (itsumo).but "main" is a first person in hindi .so, in present tense "ne"is hide in case of first person.in past tense"ne" will be coming. main bhi confuje ho jata hun "wa" aur "ga" particle men. i think it will be good after practice.