In diagrams, line segments are typically represented by a line with endpoints.
A letter is typically used to label an endpoint.
The endpoints are used for identification.
In the diagram, there are 3 identifiable line segments.
The line segments are: line segment AB, line segment AC, and line segment AD.
The line segments can also be referenced as: AB, AC, and AD.

In diagrams, rays are typically represented by a line with an arrow
extending from an endpoint. A letter is typically used to label the endpoint.
The endpoint and a second labeled point on the ray are used for identification.
The endpoint is listed first.
In the diagram, there are 3 identifiable rays. The rays are: ray AB, ray AC, and ray CA.
The rays can also be referenced as: $\stackrel{ \to }{\text{AB}}$, $\stackrel{ \to }{\text{AC}}$, and $\stackrel{ \to }{\text{CA}}$.

In diagrams, lines are typically represented by a line with arrows pointing in opposite directions. Two labeled points on the line are often used for identification.
Sometimes a diagram uses a number or a single lowercase letter, near one of the arrows, to label a line.
In the diagram, there is 1 identifiable line.
The line is line AC, and can also be referenced as $\stackrel{ \leftrightarrow }{\text{AC}}$.

Angles are often identified by 3 letter-labeled points (1 on each leg and the vertex).
The vertex point is listed in the middle.
Sometimes a diagram uses a number or a single letter, at the vertex, to label an angle.
However, a single letter label is usually not appropriate if there is more than 1 angle associated with that letter.
In the diagram, the identifiable angles are: angle BAC, angle BAD, and angle CAD.
The angles can also be referenced as: ∠BAC, ∠BAD, and ∠CAD.

acute angle	right angle	obtuse angle
less than 90°	90°	greater than 90°

parallel lines	perpendicular lines	intersecting lines
do not intersect	intersect at right angles	cross or meet

Example: