Paste dispensing is a new feature in OpenPnP that is not yet complete. To enable it you must manually edit your machine.xml.

In your machine.xml file find the job processors section. It may look something like this:

<pnp-job-processor class="org.openpnp.machine.reference.ReferencePnpJobProcessor" park-when-complete="false"/>

Add the following line so that the section now looks like:

<pnp-job-processor class="org.openpnp.machine.reference.ReferencePnpJobProcessor" park-when-complete="false"/>
<paste-dispense-job-processor class="org.openpnp.machine.reference.ReferencePasteDispenseJobProcessor" park-when-complete="false"/>

After making this change, when you start OpenPnP you will see a new tab in the Job panel called Solder Paste.

Note that currently (Apr 2021), this feature was removed from OpenPnP 2.0 as it was too burdensome to support in relation to the small number of users who used this feature in 1.0. It's currently looking for a sponsor to pick up this development again.