' vs [']
These two words are both used to get the 'xt' of a word. The word ['] is used exclusively inside a colon-def, whereas ' can be used both interactively and inside a colon-def -- but not with the same result as [']. When using the single-quote inside a colon-def, it will not find the xt of the word following inside the colon-def, but will rather find the xt of the word following when the word it is defined within is executed.

singles, doubles and floats
"Singles" and "doubles" are integer types, not narrower forms of floats.

using a "func" as an xt
It is not possible to use a "func" directly as an xt, attempting to do so will usually crash. An example of where one might try to do this is in a library onexit handler... if the library linked to has a function to de-initialize, one might think it possible to just create an appropriate "func" and use ' funcname onexit. Sadly, that does not (and cannot) work. There is an easy solution: write a wrapper:

    : shutdownlib funcname ; ' shutdownlib onexit

    :: funcname ; onexit

'' '" etc
Tokens like '" or '( (other than ''), when you see them in code are not words. Rather, they are character constants. See the tutorial's section on character input and output.