Firstly, it is important to confirm whether the person is actually chocking, you may ask him or you will see him struggling whilst putting his hand on his neck and slightly bent forward which is the universal sign of choking.
Encourage the person to cough in a bid to attempt to dislodge the object.
Put the person in a standing position, slightly bent forward whilst holding him so that he does not fall down.
If the object does not come out, using the heel of your hand, give 5 back blows in between the shoulder blades of the person.
If the person is still having much difficulty and the object has not moved and is starting to give him breathing issues, immediately call the Medical Emergency Service.
Then, position yourself between the person while attaching your hand below the sternum (breast bone) but above the navel.
You have to do abdominal thrust in order to push out the object. Firstly push inwards then upwards, inwards then upwards continuously.
Note that once you have done abdominal thrust it is mandatory to bring casualty to hospital even though the object is removed from his mouth.
On the other side, if casualty has now become unresponsive due to lack of oxygen, immediately start procedure to offer first aid to an unresponsive person