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An input port of an element is used to collect data from another element. On the Scene it A workflow element may have several input ports. On the Scene such port is displayed as prominent knob on an element with opened bubblea right semicircle.

An output port of an element is used to provide data to another element. A workflow element may have one output port or none. On the Scene it  the port is displayed as prominent knob on an element with closed bubblea left semicircle.

 A slot specifies the kind of data that can be passed through it (for example Sequence, Set of annotations, etc.)Each port has one or several slots. A slot is the smallest passageway to transfer the workflow data through. It has a certain type (e.g. "Sequence", "Set of annotations", etc.). So, for example, only sequence data can be passed through a sequence slot.

Thus, an input port has one or several input slots. These slots specify data that are expected as input by the element. An output port has one or several output slots. These slots specify data that the element produces.

In a workflow, an element usually have access to slots of the connected elements, located in the workflow before it.

A message is a single data chunk, transferred from an output slot of one element to an input slot of another element. The slots must have the same type to make the transfer possible.

The Scene is initially empty and you start with creating a workflow on it:

See an example of a workflow on the image below:

<center>
  <img src="/wiki/download/attachments/1474798/workflow_terms.png"/>
</center>

Your first step is to add necessary workflow elements, for example, by dragging them from the Palette to the Scene:

<center>
  <img src="/wiki/download/attachments/1474798/elt_on_palette_and_scene.png"/>
</center>

The added element can be moved around on the Scene by dragging it and can be resized by dragging its borders. Read chapter Manipulating Element to learn what else you can do with workflow elements.

If you have two elements with matching output and input ports, you can make the connection by dragging the arrow between the ports:

<center>
  <img src="/wiki/download/attachments/1474798/making_connection.png"/>
</center>

All matching ports of available processes are highlighted while you drag the arrow, besides the arrow sticks to a near match when you drag closer. If an element has a sole matching port, you can just drop the arrow on the element itself to create a correct connection.

Once created, a connection will follow movements of the linked elements; you cannot redirect or reshape the connection arrow but only remove it. You can move the port around an element that it belongs to by dragging it and holding the Alt key at the same time. This is helpful to fine-tune visual layout of a workflow.