Theory:

     I glared resentfully at her, and moved closer to the woman who had befriended me. Satish was standing behind his mother, grinning at me, and delighting in my clash with his mother. Apparently he was on my side.

     The station bell clanged, and the people who had till now been squatting resignedly on the platform began hustling about.

     'Here it comes,' shouted Satish, as the engine whistle shrieked and the front lights played over the rails.

     The train mowed slowly into the station, the engine hissing and sending out waves of steam. As it came to a stop, Satish jumped on the footboard of a lighted compartment and shouted, 'Come on, Arun, this one's empty!' and I picked up my suitcase and made a dash for the open door.
Explanation:
 
Arun did not like the way Satish's mother spoke to him. He looked at Satish's mother in the way of showing hatred or anger towards her. Then he went closer to the woman who spoke positively about him. Satish was observing everything happening in that place. He was standing behind his mother and watching Arun's conversation with his mother. Satish's face was filled with happiness when Arun was arguing with her. Later on, Arun understood Satish also had some kind of hatred towards his mother because she used to speak unnecessarily and Arun knew that Satish was also on his side.

The station bell rang, and the people who were waiting for the train sitting on the platform started to move quickly to get onto the train. After waiting for a long time, Satish saw the train, and he began to shout in excitement. The train slowly approached the platform. The engine made a hissing sound, and the flames of smoke came out from the engine.
 
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Smoke from engine
Finally, the train reached platform no 8. Satish rushed inside the footboard of a compartment and shouted, 'Come on, Arun, this one's empty!' Arun picked up his suitcase and dashed to the open door.
 
Meanings of the difficult words:
 
S.No
Words
Meanings
1
Resentfully
Feeling or expressing bitterness or indignation at having been treated unfairly
2
Befriended Become a friend to someone, especially when they are in need of help or support
3
Grinning Smiling broadly
4
Squatting
Crouch or sit with one's knees bent and one's heels close to or touching the back of one's thighs
5
Hustling Push roughly
6
ShriekedUttered a high-pitched piercing sound
7
Compartment A separate section or part of a structure or container
8
Mowed Moved slowly into the crowded station
Reference:
State Council of Educational Research and Training (2019). Term-3 English Standard-8. The Woman on Platform 8 - Ruskin Bond (pp. 107-114). Published by the Tamil Nadu Textbook and Educational Services Corporation.