If the app has registered a custom URL scheme the device will open the particular app when it's asked to open a URL of a particular scheme.
This stems from the CFBundleURLSchemes
key of your apps infoPlist. Apple's documentation has all the information you need to get started.
To register a URL type for your app, include the CFBundleURLTypes key
in your app’s Info.plist file. The CFBundleURLTypes key contains an
array of dictionaries, each of which defines a URL scheme the app
supports. Table 6-2 describes the keys and values to include in each
dictionary.
See more here at the iOS Programming Guide: Advanced App Tricks under 'Communicating with Other Apps' section.
Edit
In order to support the specific functionality of your question you need to go one step deeper.
- Your first link needs to be a standard web URL.
- The page presented from the first URL needs to detect the device and forward the user onto a second URL that will open the app on the device, with whatever parameters you want to forward to the app.
So - what you're going to have to do is build some sort of device detection into the page that your first URL points to. On that page, detect the device, then conditionally forward the user onto the second URL that will be the custom URL of your particular app.
It's possible to do this device detection, and detect if they have the app installed on their device with some of the newer HTML5 features supported by mobile browsers, but your question is themed around opening apps with URLs in iOS and the main native iOS hooks you need to support opening apps (with parameters and all) is in the documentation above.