68 The definite article here is the generic use; it simply refers to a group of shepherds.
69 The actions of the shepherds are subordinated to the main statement about what Moses did. The verb is וַיְגָרְשׁוּם (vaygorshum). Some shepherds came and drove the daughters away. The choice of this verb in the narrative has a tie with the name of Moses’ first son, Gershom. Moses senses very clearly that he is a sojourner in a strange land—he has been driven away.
70 The verb used here is וַיּוֹשִׁעָן (vayyoshi’an, “and he saved them”). The word means that he came to their rescue and delivered them. By the choice of words the narrator is portraying Moses as the deliverer—he is just not yet ready to deliver Israel from its oppressors.

In other versions

The shepherds came and drove them away, but Moses stood up and saved them, and watered their flock.

Some shepherds came along and drove them away, but Moses got up and came to their rescue and watered their flock.

Then some shepherds arrived and drove them away, but Moses came to their rescue and watered their flock.

But some other shepherds came and chased them away. So Moses jumped up and rescued the girls from the shepherds. Then he drew water for their flocks.

And the shepherds came and drove them away, but Moses stood up and came to their rescue and watered their flock.

And the shepherds came and drove them away: but Moses stood up and helped them, and watered their flock.

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