@Timur_Akhmadulin Hey, If you are doing some exercise from MongoDB University you must have seen the complete connection string in the previous lecture(s). By adding the complete string you can connect your system to their server.
For example the connection string for basic course is as followed:
mongo “mongodb+srv://cluster0-jxeqq.mongodb.net/test” --username m001-student --password m001-mongodb-basics
If you still have some confusing you can share the course link so that we can send you the connection string (if you are connecting your system to their server)