How to access the Library folder
Your title does not seem to have anything to do with your actual question, you should change that.

There are a number of "Library" folders on your Mac, but the only one you should ever go into is actually hidden, meaning that Apple (for all intents and purposes) recommends you stay out of it. 

Why? Because deleting things in your users Library folder without knowing what these files do could cause more than a few things on your Mac to stop working.

If you just need to do some clean-up and delete unneeded files I recommend using a utility like Onyx (I use it, there are others that do similar things). And that will clean up the unneeded (cache and temporary) files for you, safely and easily.

If you want to go exploring though you can view  your Library folder by holding the Option key down while selecting the Finder's "Go" menu. "Library" will show up in the list and then all you have to do is select it to open a Finder window to explore.

But, again, be careful deleting things. If you do not know EXACTLY what a file is or does leave it alone or you could cause problems with your Mac, one or more of your Apps or numerous other things could stop working.