here mainly, i can tell you right here and now, that the "hd" stands for "hard drive" and that stores information, like the operating system(s), files in general.
"mobo" stands for "motherboard" it just kind of holds all the componants together, without a motherboard everything would be useless by itself.
and for "ram" that stands for "random access memory" basically it just stores some information(i've never figured out what exactly) but, everytime the computer loses power(shut down), it loses all that information.
i guess wikipedia would be another place to look