Timelines: more information

Hi there,
I am currently working on my assignment about Timelines in English grammar, but I am having a problem locating information on topic. In my assignment, I have to link up sentences (which are simple past, future continuous and so forth) to a timeline chart, and some of the charts have two x's or squiggly lines, or 3 strokes. It has left me a little confused.

It would be great if someone could direct me in the right direction.

Thanks for your help.