In revelations, the wording is a little confusing about just who these beings are. But Daniel says it more clearly.

A thousand, thousands served him,
and ten thousand times ten thousand stood before him.

A thousand thousands, that is, one million, serve him. The angels serve him. There may be many types of angels, but the ones that serve him directly are different. White robes with gold sashes. There are more than just one million angels. There are angels that are involved in general tasks. There were the watchers from before the flood as well. And the third of the angels that fell with Satan. Almost certainly, these were cherub angels.

The 100 million are those who died during the tribulation and those who have given their lives for God earlier on. An exact confirmation of the figures in Revelation.