Units of acceleration are typically m/s^2 (meters per second squared). Time is typically in seconds. So when you multiply (m/s^2) by (s) the results is (m/s) or, meters per second (which are the units for velocity). Multipying acceleration by the change in time gives you the change in velocity. Here's an example.
If a car is accelerating at 10 m/s^2 for 5 seconds, then 10 m/s^2 * 5 s = 50 m/s. So, there is a 50 m/s increase in velocity. But you still don't know the absolute speed of the car because you don't know it's starting speed. If the starting speed was 2 m/s then 2 + 50 = 52 m/s absolute speed.
Now let's say you have vectors of data where each element of the vector was recorded at different time points.
acceleration = [0 1 1 2 2 2 5 5 5 2 2 1 1 0];
dt = 0.2;
The instantaneous change in velocity would be
dtVel = acceleration .* dt;
And the absolute velocity would be (assumes velocity starts at 0m/s at time 0)
View the data
time = dt * (0:length(acceleration)-1);
figure; plot(time, acceleration, 'b-', time, vel, 'r-')