how to change directory in Terminal (ex. cd System HD)

You need to escape the spaces with a leading backslash or the shell will give you unexpected results.

For example to cd to "folder with spaces"

cd folder\ with\ spaces/

Also, the bash tab-auto-complete is your friend. Type a character or two and then tab, you'll get the idea when you see the result. If there is more than one possible completion, then hit tab a couple of times quickly and you'll get a list of all of the options.

hth

As an aside, parenthesis also work when spaces are present.
I do it using the wildcard *
In your example, cd *fold (of course it has to be a unique folder/filename)
That comes from years of Linux training and a strong dislike of typing.