missing left hand column - original settings

I'm just starting to use ZoHo and really like the product. When I initially logged on, the apps (docs, sheets, etc) were in a left hand column on my desktop. Therefore when I logged on to ZoHo I had three columns - (from the left) - one column with the apps, the next with the particular app info such as documents available, and the third column (the biggest) contained what I was working on.

So, I'd click Sheet, my folder/document list would open up in the second window, click a document, and it would open in the third window. Great stuff!!

Now, unfortunately, I can only access the apps in a 'Switch to' drop down menu on the top of the bar, and everything I select opens in a new window. I must have change some setting somewhere, but can't find it.

How do I get back to my original settings?

Thank you, Tom Campbell