Wow, that's pretty hard to answer. Lol. I suggest you try to just use it learn in by using it. Also google is good for finding answers to your problems and Microsoft sites has a good tutorials etc.
I think you have to read the Help section, you can find all your q? and answers in the help section. Thanks
Try to read some of the instructions in the help options to learn more or read more topics over the net.
Practice makes perfect especially ms.office itself is extremely user friendly. When there are rare moments you have any issues on, click on their help wizard or do a Google search.
you have to choose a part according to your usage e.g. MS Word and try to learn its functions by reading books upon or tutorials upon it. Once you master a field than it won't be quite difficult for you to master others because rest have only a few functions different. So first try to master one.