Acceleration-time graph

One reading matters, and getting it slightly wrong is the whole trap.

Area is the change in velocity. EK 1.3.A.4.iv states that the change in velocity of an object during a time interval equals the area under the curve of a graph of the object's acceleration as a function of time. The area hands you $\Delta v$. To turn that into a velocity you have to add the velocity you started with, $v = v_0 + \Delta v$, and the graph does not tell you $v_0$. Two objects with identical acceleration-time graphs can be moving at completely different speeds throughout.

Signs matter for the same reason they do on a velocity-time graph. Area below the time axis is negative and subtracts from area above it, so a graph that is symmetric about the axis leaves the object at its starting velocity.

Units confirm the reading. Vertical axis in m/s$^2$ times horizontal axis in s gives m/s, so a rectangle means constant acceleration $a$ for a time $t$ changing the velocity by $at$.

Nothing is read off the slope. No AP Physics 1 essential knowledge statement assigns a physical quantity to the steepness of this graph. Slope readings in the course belong to position, velocity, momentum and angular momentum graphs.

Common shapes: free fall is a horizontal line at about $-9.8$ m/s$^2$, an object at constant velocity sits flat on zero, and a collision draws a tall narrow spike whose area is the change in velocity the collision produced.