There are two types of angles: acute angles and obtuse angles. An acute angle is one that is less than 90 degrees, while an obtuse angle is one that is greater than 90 degrees.
A corner is simply the point where two lines meet. An angle is formed when two lines intersect at a corner. The angle is the amount of space between the two lines at the corner, and is measured in degrees.
So, to recap: an angle is a measure of space between two lines at a corner, and is acute if it is less than 90 degrees, and obtuse if it is greater than 90 degrees. A corner is simply the point where two lines meet.