I bought a note (owner financed loan) on a piece of land. How do I account for the investment and monthly income it generates on my taxes?

If the monthly income is the repayment of your capital plus interest, then you need only to report the interest income on your return.  You will issue a form 1098-INT to the person who is paying you the interest.  This form is due to the IRS on January 31 of each year.

If you paid less for the note than the capital repayment (e.g.  you paid $8,000 to receive $10,000 in capital repayments, plus interest)  then you will record an installment sale on your return, if the payments will come over two or more tax years.

To record an Installment sale in TurboTax:

• Click on the Search Box and type "Installment Sales" in the window, then Enter
• Choose "Jump to Installment Sales," which should be the first result
• On the page "Any Other Property Sales" select the box for "Sales of real estate, cars, or anything else for which you receive payments over two or more tax years (installment sales)" and Continue
  
• You may be prompted to upgrade
• On the Installment Sales page answer Yes to "Do you want to report an installment sale?"
• Continue through the interview and record the details of your Installment