If you are accessing Moodle using an iPad, iPhone, or iPod touch, there are a few things that the web browser can't do, such as uploading files. If you are using an Android or Blackberry device, the browser will work, but for iOS you might need an app.
The official Moodle app is free, but is only optimized for iPhone and iPod touch. It allows you to make and upload audio recordings, pictures, and videos to your "Private File Area" so that they can be submitted as assignments or attached to posts. As an example, you could use the camera on your device to take a picture of a written assignment.
Paid apps that work with our server are mTouch for iPhone/iPod touch, mTouch+ for iPad, and moodlEZ for iPad. These do the same things as the official Moodle app, but also allow you to download and upload files in conjunction with apps such as Evernote and Dropbox.