Tasker is an automation app for Android. It lets you automate the execution of actions based on triggers like time, location, other apps, ...
In this sample scenario, we won't be using a trigger but just create an action that will let us control a switch in OpenHAB.
OpenHAB has a REST API that you can use to integrate OpenHAB into other systems (like your own front-end website).
To keep things simple for this exercise, we'll just use a very simplified version where you don't need to post anything. You can find it at /CMD on your OpenHAB site. For example, if OpenHAB is at 192.168.1.80 and you have switch item named KanKun then you can trigger the switch with these URLs:
Using Tasker, you can add a widget on your Android phone that you can click to toggle the switch between On and Off. If you have an Android Wear watch, you can even add it to your watch!
Step 1: Open Tasker and add a new Task
Step 2: Give the Task a name
Step 3: Add an HTTP GET Action to the Task
Step 4: Use the filter at the bottom to help find the right Action
Step 5: Break up the URL into 3 pieces & remember to change the IP if yours is different
Step 6: Give the Task an Icon and (optionally) add a second "Flash" Action.
Then exit "Task Edit" by clicking on the Tasker icon in the top left
Step 7: Go to the home screen you want to add the widget to and open the widget locker
(in Lollipop you do this by long-pressing on some empty background)
Step 8: Click it! Click it again!
It doesn't do all that Tasker does, but if you just want to create shortcuts for your switches then it does the job just fine.