Guideline: Most biology found in the galaxy has a corollary with Earth biology. This just keeps me from having to invent things in fields I know enough about to know I will only be hilariously wrong.
Biology across the galaxy is, as far as anyone's been able to tell, roughly uniform. Exactly why life across the universe all seems to roughly fall inside the same rules is hotly debated; some feel that it's really just the law of averages: there's only so many ways to tackle the same problems, and the solutions we are familiar from on earth just happen to be the easiest, on average, so everything looks like Earth life, on average.
(Other schools of thought tend to bring religion, mysticism, or both into it.) Whatever the reason, it turns out that life seems to all be carbon-based, with rough analogs to the types of life found on Earth.
Insects are as universal, it seems, as they are despised. A 'near insect' is any small invertebrate animal, especially one with several pairs of legs.
Most sentient creatures are 'near mammals', i.e. a warm-blooded vertebrate animal of a class that is distinguished by the possession of hair or fur, the secretion of milk by females for the nourishment of the young, and (typically) the birth of live young.
The term "humanoid" is often to refused to creatures that are morphologically similar to Humans. Typically, humanoids are roughly human in height and weight, with two eyes, to ears, two arms, two legs. Often they have recognizable reproductive organs and are near-mammals, meaning females generally have two discernable breasts, and males generally do not.
The comparison is mainly visual; there's no actual biological similarities required to be considered 'humanoid', the creature just needs to look like a human if you squint.
'Near reptiles' are vertebrate animals that are distinguished by having a dry scaly skin and typically laying soft-shelled eggs on land.