Big endian – most significant byte stored in smallest address,  read from left to right.

Let’s take a 32-bit value :

0x09080706 :

09|08|07|06

byte address : x|x+1|x+2|x+3

For example 32-bit value 5 writing as 0x00000005 is a Big endian.

Little endian – least significant byte is stored in smallest address, read from right to left.

32-bit value would be stored in memory in following way :

0x09080706 :

06|07|08|09

byte address : x|x+1|x+2|x+3

For example little endian value would be 16-bit value 53  in 0x3500

Useful info about this :