As someone said up the thread, what exactly is it about this topic with which you are struggling? The basic concepts are easy: substances (be they atom, molecules, ions or whatever) react in certain ratios, and so it is necessary to know how many of the reacting 'particles' you have of each thing which is reacting. You can't just weigh things, because atoms, molecules etc all weigh differently. Thus, there is a concept called the mole which is the SI unit of 'amount of substance' - this is 6.022x1023 'particles'. Note, this is just a way of referring to a specific number of 'particles' - you could have a 'mole' of cars, a 'mole' of moles, or a TSR A level student who has a 'mole' of Grade 9s at GCSE (Oxbridge's standard requirement for admission).
Once you've got a handle on this, start to think about what it means if I tell you that 12g of carbon contains one mole of carbon atoms. What is the Ar of carbon? And can you see a relationship between that and the Ar of other elements, and how that could help you use the concept of mole when considering chemical reactions?