Though 'a group of ladies' or 'a group of dogs', are both grammatically correct, 'group' is rather mundane, and often used when we don't know the collective noun for the object we're referring to. A collective noun is the word we use to refer to a group of things such as people or animals. Words referring to groups of animals are also known as terms of venery, e.g., a pride of lions, a pack of wolves.
Having said that, however, some collective nouns are not commonly used, and are considered fanciful or humorous terms, e.g., a blush of boys or a pity of prisoners, and some words can have more than one valid collective noun, e.g., a cohort/herd/zeal of zebra. Similarly, the same collective noun may be used for different objects, such as a flock of seagulls/sheep/camels/pigeons/etc..
I've created a few games here. The elementary learners can do the animal identification game quite comfortably, and if they are adventurous enough, they can try the others, too.
Identify these animals Part 1
Identify these animals Part 2
What are the collective nouns for these animals Part 1?
What are the collective nouns for these animals Part 2?