Explain Upnishads Vedic Literature

A few important points about Upanishads are mentioned below:

# There are 108 Upanishads
# Out of 108 Upanishads, 13 are considered the major ones.
# The concepts of ‘Atman’ and ‘Brahman’ are majorly explained by Upanishads.

It contains philosophical ideas about the following concepts too:
# Sacrifice
# Body
# Universe