You cannot relate records from the same object via an relationship field.

What are the 3 types of custom tabs?

What is a custom Application?

What is a page layout?

Building your User Interface How can you control the different settings of the page layout?

What is a cross-object formula?

When a cross object formula references currency fields of a different currency to that on the
record where the formula is used, Salesforce randomly picks one currency to use.

What is the limit for cross-object formulas?

You cannot reference cross-object formulas in roll-up summary fields.

Describe a roll-up summary