While I'm at it, let me do a little spadework on ST I-II, qq 8-16, a schematic of which I gave in a post the other day.
We humans can want things. We can want things we see, touch, hear, taste, or smell, and we can want things we think of. The power to want things we think of is called the will.*
So "the will" is a power we have, and according to St. Thomas this power to want things acts in two ways: it can act immediately; and it can act by commanding other powers to do things (ST I-II, 6, 4).
St. Thomas distinguishes six different immediate acts of the will; three are in relation to the end, and three are in relation to the means:
Volition is the act of wanting some end. This is the "simple act of the will" we mean when we say "I want" or "I will that."**
Intention is the act of wanting some end by means of something else. Where by volition I simply want something, by intention I want to do what it takes to obtain what I want.
Enjoyment is the act of... can I just say it's the act of enjoying some end?***
Consent is the act of approving some means to an end. (The means is identified by the intellect by an act of counsel.)
Choice is the act of wanting a particular means to which consent has been given.
Use is the act of executing the chosen means by application of the appropriate powers under the will's control.
Skipping the activity diagrams for now: An act of volition ("I want a donut") precedes an act of intention ("I want to get a donut"). If the act of volition concludes successfully, an act of enjoyment may follow ("Yum!").
As for the means: Acts of consent approve of certain means identified by the intellect ("I can buy a donut," "I can make a donut"). An act of choice selects the particular means ("I can buy a donut"). Acts of use then carry out the means ("...now I'm reaching for my wallet...").
A final note: For each of these acts, St. Thomas asks whether irrational animals are capable of them, and concludes that they are not. These questions are relevant because St. Thomas considers all of these acts to be "acts pertaining to man," and therefore more closely associated with our final end than those acts that pertain to both humans and the other animals.
* To get fancy, the power to want something is called an "appetite," the power to want something we can sense is the "sensitive appetite," and the power to want something we can think of is the "intellectual appetite." To get really fancy, we don't just sense things, we "apprehend them by sense," and we don't just think of things, we "apprehend them by intellect" or "by reason."
** A variant of volition, which St. Thomas mentions just once, is "nolition," the act of not wanting some evil end. I think I see why he mentions it, and also why he doesn't mention it again.
*** If you like, you could translate St. Thomas's "fruitione" as "fruition" instead of "enjoyment." At least that way, you can say "fruition is the act of enjoying some end," and feel like you've said something nontrivial.