Your account supports two types of sales targets: Individual targets and Rollup targets. You can only have one of each.
As the name suggests, individual targets are for the individual team members they are assigned to. To create an individual target make sure the Rollup checkbox in unchecked. Although you can add multiple targets, only one active target is supported at the moment.
A rollup target is only used when you have other team members reporting to you. When you select the Rollup View from the home page, this is the goal used on the YTD and Pipeline charts.
You can set monthly, quarterly or yearly target periods. Just pick the frequency period which best suits your particular situation.
If you are starting from scratch, set the start date to the current month. The home page will then only count from this month onwards. If you are migrating from another system and will be importing existing deals you might want to back date the target. You can change the target at any time from the members section in the admin panel.