What are the Ānāpānasati Kammaṭṭhāna as Taught By Ven. Kiribathgoda Gnanananda Thero
Mainly it is concentrating on one's breath as "l'm inhaling short, I'm exhaling short" or otherwise "I'm inhaling long, I'm exhaling short". 

This is what Lord Buddha asks us to do in the beginning. He also says this meditation isn't for everybody. This meditation isn't the only way to understand the Four Noble Truths. 

Official Website: http://mahamevnawa.lk/

Meditation Section: 
http://mahamevnawa.lk/meditation/

You can find English sessions of Sound Cloud in that website and might find English guides on meditation. 

The thero also published a book in sinhalese called É Ama Nivan Suwa Bohoo Dura Nowe (ඒ අමා නිවන් සුව බොහෝ දුර නොවේ - The Nirvana is not that far away) which explains Maha Satipattana Sutta, which contains the above form of breathing. Buddha states also to note that the breath isn't me, mine or my soul (hence the book contains it).