What counts as data/storage on iphone 4s?
Yes, to view the current storage being used, you can navigate to Settings > General > Storage &amp; iCloud Usage > Manage Storage.    From here, you can see which apps are taking up a lot of space, how much space your photos / music are taking up, etc.

Once you know what's taking up all your space, you can delete things as needed.

Also, note that in older versions of iOS (depending on which you are currently on), space taken up by Messages was not shown here.