Parameters can be used to set up specific values that can then be called on expressions and filters within the dashboard.
Firstly, open a dashboard in the dashboard designer.
The dashboard below, in its current state, displays each Sales Order document number per customer. Lets add a Parameter that gets the Customer's Name in order to filter by Customer Name.
Navigate to the 'Home' tab on the Dashboard Designer. Click the 'Parameters' button. 
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This will open the 'Parameters' menu. Click 'Add' to add a new Parameter, named 'Parameter1' by default.
Choose a 'Name' and a 'Description' for the Parameter. The 'Name' is important, this will be the name to call this Parameter by within expressions. The 'Description' defines how the Parameter will be displayed on the front-end of the dashboard.
We want this Parameter to be set as one of the customers. We can make it so that the options for this Parameter are a drop-down menu containing the Customer Names. Set the 'Look-Up Settings' to 'Dynamic List'.
Selecting 'No Look-Up' will allow users to enter manually the value for the Parameter. Selecting 'Static List' will allow you to manually set each option to be available to the Parameter.
On the left side of the Dashboard Designer, we can see the 'Data Source' available to the Dashboard. For the 'Dynamic List' set the 'Data Source', 'Data Member' and 'Value Member'
- Data Source
This is essentially the database that the dashboard is pulling data from, it is listed as the SQL query generated when creating the dashboard. - Data Member
This will be one of the tables called in by the SQL query data source. - Value Member
This will be a field from one of the tables called in the SQL query data source.
The other settings such as 'Sort By' and 'Sort Order' apply to the drop-down list of the Parameter. The 'Value' setting is the default value to be set for the Parameter. Click 'OK' to confirm.
To view the Parameter on the front-end, click the 'Parameters' button found on the top-right of the dashboard. 
The 'Dashboard Parameters' menu will open up. This is where you will set your Parameter value when using the Dashboard.
To finish setting up this Parameter, we need to create a global filter on the dashboard that looks at the Parameter value.
Select the 'Pivot' on the dashboard and navigate to the 'Data' tab and click on the 'Edit Filter' button.
This will open the 'Filter Editor'. The name of our Parameter Value was set to 'Customer', in order to call it in the filter expression we start by using a question mark '?' followed by the Parameter's name. The expression below states that the filter must display values only where the 'Name' field from the 'Account' table equals the name provided in the Parameter value.
Now selecting a Customer from the Parameters will filter the pivot to only display the selected customer.
