We recommend the following useful text functions if you are looking to take sheets data and build usernames or passwords:
=CONCATENATE(string1, string2) or the "&" argument to glue together string values.
=LEFT(string, N) to pull the leftmost N characters from a string.
=RIGHT(string, N) to pull the rightmost N characters from a string.
=LOWER(string) to drop a string into lowercase
=RANDBETWEEN(lowNumber, highNumber) to generate a random number between two numbers