Not picking on you! This is just one of the most over asked questions here. A good start for newbees are the FAQs.
Right from the VJ Wiki...
What is a touch? Any time your application is handled by someone at a Service Center, the barcode is scanned, which results in an update to the "last date" for your case on the
USCIS website. When the date changes, this mean that someone has physically handled or "touched" your case. There are many reasons your application may be "touched" - from simply being moved from one desk to another, to
RFE's, to being approved.
There are 2 kinds of touches. There are the ones that show some kind of update, there are the ones that don't bring a new message. By logging into the account, take a look at the date that shows next to your case number. If it's changed, you've been touched.
By clicking on the case number, you get to check whether it was an update touch or not. The ones that don't show updates are connected with some kind of work done with regard to your case - it merely shows that they've taken a look at it somehow.