What is an angle?

An angle is the space between two intersecting lines or surfaces. Angles are typically measured in degrees. An angle is also used to measure the amount of a turn.

There are six main types of angles:
Acute: Angles that measure less than 90 degrees
Obtuse: Angles that measure greater than 90 degrees, but less than 180 degrees
Right: Angles that measure exactly 90 degrees
Straight: Angles that measure exactly 180 degrees
Reflex: Angles that measure greater than 180 degrees
Full Rotation: Angles that measure exactly 360 degrees.

For additional information and practice, the following links could be of assistance:
https://www.mathsisfun.com/angles.html
https://www.khanacademy.org/math/basic-geo/basic-geo-angle

Just think of two straight lines. Either they will be parallel or going to intersect each other .
First we will try to understand what is angle roughly.
Angle measures the bending of a line towards another line . That is how much a line is inclined towards other line. The unit of angle is degree or radian. Angle is also used to measure of a rotation. This measure is the ratio of the length of a circular arc to its radius.

1 radian is defined as the angle formed by arc, of length circle's radius , at the centre of circle.
We can observe that circumference of circle is 2πr and this circumference form 2π radian angle at centre of circle with radius r.
The relation between degree and radian is given as
180° degree =π radian.
Angles formed by the intersection of two curves in a plane are defined as the angle determined by the tangent rays at the point of intersection.

An angle is a geometric figure constructed of two rays with the same endpoint.An easy way to think of it would be the sun, and how the sun has "sunrays." All of those sunrays, if you were to draw them, would start at the center of the sun. Pick two of them, then the "space" in between them is an angle.The attached link provides a diagram of some common angle types. Pay attention to all the information there, not just the pictures. For instance, with the supplementary angles, it says below the angles "a+b=90." That is important; "a" and "b" are the angles, and for them to be supplementary, they would add up to 90 degrees if you were to combine them (i.e., add them together). So, those statements under several of the angle pictures are just as, if not more, important as the pictures themselves.