I'm a novice at this function.

We send money to the department of revenue for each state. Each state has
an assigned "account" number. My spreadsheet has a column in which a state
abbreviation should be typed. If I enter the state abbreviation "MO", I
would like to have the corresponding "account" number appear in the adjacent
cell.

Is this the best function to use? And, if so, how do I get it to work? I
keep getting error messages with this.