After you create a local or global variable, you can read data from a variable or write data to it. By default, a new variable receives data. This kind of variable works as an indicator and is a write local or global. When you write new data to the local or global variable, the associated front panel control or indicator updates to the new data.
You also can configure a variable to behave as a data source, or a read local or global. Right-click the variable and select Change To Read from the shortcut menu to configure the variable to behave as a control. When this node executes, the VI reads the data in the associated front panel control or indicator.
To change the variable to receive data from the block diagram rather than provide data, right-click the variable and select Change To Write from the shortcut menu.
On the block diagram, you can distinguish read locals or globals from write locals or globals the same way you distinguish controls from indicators. A read local or global has a thick border similar to a control. A write local or global has a thin border similar to an indicator.