A line is a one-dimensional construct that extends into infinity in both directions. A line segment is a section of a full line. A line segment is usually displayed on a page with dots on both ends. These dots are referred to as endpoints. The endpoints will indicate that you are looking at a line segment. If you were looking at a line, the ends would have arrows.
A ray is a combination of a line segment and a line. A ray has one endpoint, indicating that it stops at this location while the other end has an arrow head to indicate that it goes off into infinity. Like a line segment, a ray is one-dimensional and has no width. It cannot be measured because it travels to infinity in one direction.
An angle is nothing more than two rays that share the same endpoint. Think of the corner of a table. The shared endpoint is where two sides meet to form the corner. In geometric terms, the edges would then travel off in opposite directions into infinity. The point where the rays intersect is referred to as the vertex, and the two separate rays are the sides of the angle.
Angles are measured in degrees. If you were to draw an imaginary line from 9 to 3 on the face of your watch, this would be a 180-degree angle. If you were to move left side of the line from 9 to 12, forming an "L" shape, you would have a 90-degree angle. Every time one ray of the angle moves closer to the other ray or farther away, there is a change in degree. Any angle between 0 and 90 degrees is referred to as acute, and any angle between 90 and 180 degrees is considered obtuse.