Firstly, students should be able to define what parallel lines are. Parallel lines are two lines that are always the same distance apart and never meet, no matter how far they are extended. They can be represented by the symbol '||'.

Students should also understand the properties of parallel lines. For example, parallel lines have the same slope and never intersect. They should be able to identify parallel lines in diagrams and real-life situations.

Next, students should understand the relationship between parallel lines and transversals. A transversal is a line that intersects two or more lines at different points. When a transversal intersects parallel lines, it creates a set of corresponding angles, alternate interior angles, alternate exterior angles, and consecutive interior angles. Students should be able to identify these angles and understand their properties.

Finally, students should be able to solve problems involving parallel lines and transversals. They should be able to use the properties of these lines and angles to find missing angles, determine congruent angles, and prove geometric relationships.

In summary, understanding parallel lines and their properties is a key aspect of geometry for grade 8 students. By learning to identify and work with parallel lines and transversals, students can build a strong foundation in geometry and problem-solving skills that will serve them well in their future studies.