Tags are a very flexible way of marking a sales order or purchase order with a tag you can easily see. For example, say you want a way to easily track which purchase orders are approved before they can be sent. You can create a tag called "Approved", and then you can tag each approve PO as Approved.
Since you can create the tags and make them any color, this is just a flexible way of tracking something about certain sales orders or purchase orders.
First, you need to create a tag. Head over to the tag manager under Settings > Tags. From here, click New Tag to create a new tag. Give the tag a name, a description, set the color, then specify the tag type.

In this case, we want this tag to be applicable for purchase orders, so we set the tag type as Purchase Order. The name of this tag is Approved since we want to tag a PO as approved.
Here we can see a handful of tags that have been created:

First we will take a look at adding tags to a sales order. On the top right of the sales order, you will see a little Tag button. Click this button to select a tag:

Let's say we often attach a custom sketch or drawing to a sale so we can keep track of it, but the customer did not have the document on hand. We want to add a tag to this sales order to remind us that we still need to attach the sketch to this sale.
Here we have chosen the Attach Sketch tag.
Once saved, the tag is clearly visible on the top right:

On the Sales Orders list, we can also see the tags applied to sales orders:

To remove a tag, just open the sales order and click the little x on the right side of the tag.
Tags for purchase orders are very similar, except they can be added from the Options menu on the top right of the purchase order:

Once added, we can now see the tag(s) applied to this purchase order:

Then on the purchase orders list, you can see the tags applied to any purchase orders:

Remove a tag by opening the purchase order and clicking the little x, same as on a sales order.
You can add multiple tags to a sales order or purchase order, you are not just limited to one. The sales order history and purchase order history tabs will show any time a tag has been added or removed, so you can always track who added/removed the tag and when it was done.
