docker run -d \
  -e MONGO_INITDB_ROOT_USERNAME=admin \     # creates user
  -e MONGO_INITDB_ROOT_PASSWORD=changeme \  # creates passwd
  -p 27017:27017 \
  --name my-mongo-container \
  mongo --auth  # starts mongodb with authentication enabled

Create new database and its users:-

test> show dbs
admin   100.00 KiB
config   12.00 KiB
local    72.00 KiB

test> use schooldb
switched to db schooldb

schooldb> db.createUser({user:"user1",pwd:"changeme123",roles:["readWrite"]})
{ ok: 1 }

admin> db.system.users.find()

docker exec -it my-mongo-container mongosh -u user1 -p changeme123 --authenticationDatabase schooldb

db.students.insert({ name: "john doe" })