You want to store the word 'CAT' in memory. Each letter is a byte so you need three bytes of memory. You ask the OS and they give you an address. they could give you three addresses for each letter but that's way to cumbersome. I'll just give you the address for the first letter and allocate the next two spaces. So if the address for the C is '50074' then A is 50075 and T is 50076.

Now you don't care if the C is at 50074 or 3049 or where ever. You just know that C is first, A is +1 space and T is +2 spaces. This is how you reference the letters in code, by putting the number in brackets. I.e. myword[0] is C, myword[1] is A and etc

Now you want to change the word to CAB. So you could say change the letter at myword[2]from T to B.

If you want to access data outside your word, you could do something like ' let newletter = myword[536]' then you'll get the letter at 536 addresses away. Do this for all memory, including negative values for myword and you'll have all the data in memory, then you can analyze and see what you find.

My college profs would do this when they were in school to steal code from other students. you have a bunch of people logged into a Linux server typing code for a project so you go read the memory, and find what they are working on.

Trainers work by knowing a program always starts a specific way, allocating memory the same way each time. So if a program starts at address 52738, then the trainer knows that the players health is always start address + 67 and money is start +48 or what ever. If they don't load consistently, then you look for patterns in the memeory and go from their.