Follow the below steps for further integration :

Step 1

First of all you need to download engap plugin from GitHub or from /
Install and activate this plugin in you ELGG webiste.
for Elgg make sure that webservice is working(in latest ELGG its made a separate plugin)

Step 2

Download enGap app from play store/App store or click here to download enGap Application.
enGap enGap
Configure the app with your site URL and site name.
Login to your site with your username/password