All 3 Uses

focus
in
The Giver
(Edited)

He realized, though, that not focusing on one area meant he was left with not the slightest idea — not even a guess — of what his Assignment would be.
p. 29.2

focusing = concentrating
He felt dizzy, and couldn't focus his attention.
p. 57.5 *

focus = concentrate
He watched the landscape for glimpses of the green that he knew was embedded in the shrubbery; when it came flickering into his consciousness, he focused upon it, keeping it there, darkening it, holding it in his vision as long as possible until his head hurt and he let it fade away.
p. 106.4

focused = concentrated

Definitions:

(1) (focus as in: Turn your focus to question #2.)
to direct attention or effort toward a single thing; or the ability to do so without getting distracted
(2) (focus as in: The focus of our study is...)
where attention is concentrated or directed
(3) (focus as in: bring into focus; or out of focus)
a state where something has come into view or can be seen clearly; or an adjustment made to permit a clear view
(4) (focus as with technical usage)
technical usage typically involves some sense of center or concentration such as:
- physics — a point where things come together such as the point where light rays meet
- geometry — a fixed reference point (as of a parabola)
- geology — the point of origin of an earthquake
See a comprehensive dictionary for other less common meanings.
(5) (meaning too rare to warrant focus)