When we tell a story, we have to choose how much detail to go into.
If we summarise action, we’re just telling the key points and not going into any detail.
For instance, this snippet summarises an entire fight, from beginning to end.
When he confronted Aaron, a brutal battle ensued. Aaron got the best of Miles, who was still just a novice at using his powers, leaving nothing but the final blow of one of Aaron’s electric gloves, called gauntlets. But the gauntlet malfunctioned and blew up in Aaron’s face, leaving him crushed by an explosion he’d planned to use, in a desperate fit, to kill Miles.
The snippet skims over most of the details. It doesn’t tell us how Aaron got the best of Miles, or how Miles felt about it, or the look on Aaron’s face when his gauntlet malfunctioned. It just says, they had a fight, Aaron was winning but then his glove blew up.
That’s summarising action.
The next day passed like any other. Alexei opened up the store before the sun had even risen, put on coffee for the regulars and organised the stock. The sky grew darker towards the afternoon, so he packed up early to make it home before the snow set in.
It was all fine until the rats came. First they took over the cupboards, then the oven, until finally they were spilling out on the floor. Henry had expected the cats to do something but they’d turned out to be useless and he’d had to call for help from the creepy guy with the python at the end of the hall.
We summarise action when we don’t feel like the details are important. We just want the reader to understand what happened, so we can get onto some action that we do think is important.