Hi Abby,
From what I can see in your pictures, you have something very similar to what is in my basement right now for my 2 kids (3 and 6 yrs). It looks like you have two 2x4 foot sections with the long edges together.
As I contemplate doing a Christmas layout, I was thinking about modifying my 2x4 modules to each be a "1/2 donut" shape. That way, the tree can poke up through the middle, while still giving enough real estate to do a convincing Christmas village and train track.
The two halves can then be taken apart and boxed together for storage until next Christmas.
As David said, the easiest way to get the cars hooked together ("coupled") is to put each on the track separately, and then push them together. The couplers should automatically engage. To get them apart, push the cars towards each other to create some slack, slide a small screwdriver between the couplers and twist them apart. Or you can simply lift one car up and set it back down somewhere else...
Hope you're having fun...!
Andrew