Configuring your product library allows you to get more insight into the total amount on a quote, as well as view ARR associated with each deal. ARR may be distinct from the normal Amount value on contracts that aren't 12 months or include non-recurring revenue.

Click the 'Gear' in the top right hand corner. Underneath Data Management, expand the Objects, and select Products.

For each product, fill out the Product Name, Unit Price, and Billing Frequency. Note that billing frequency does not represent payment terms - it is the unit of time that the unit price applies to (i.e. $600/mo or $600/yr). Also note that products with a Billing Frequency of One Time are not factored into calculations of ARR.