Theory explained in text

Alternate angles.
When you have two parallel lines and a line that intersects with those you can see a Z shape. Like in the figure to the below:

Now If you have the Z shape in a figure (remember you have to have a set of parallel lines!) You can use the rule of alternate angles. Which is: Alternate angles are equal.

Here are some more examples of alternate angles and some non-examples:

 

Corresponding angles.
When you have two parallel lines and a line that intersects with those you can see a F shape. Like in the figure to the below:

Now If you have the F shape in a figure (remember you have to have a set of parallel lines!) You can use the rule of corresponding angles. Which is: Corresponding angles are equal.

Here are some more examples of corresponding angles and some non-examples: