For example, you can have a table within a table. To see this, look at the menu on the right. You'll notice that the cell lines are much finer. That's because it's another table within the main one. This helps with lining up the images.
Tables are one of the more elaborate tags, they have lots of elements, and lots to understand.
The one below uses a gap of 5, and a border of 2. The below example uses a gap of 10. You can also individually colour tables or rows. Here's the tag for that last table, just the table tag mind. That's just the enclosing tag, then you have to define the data itself.