The first rule is applying the tax by using an Order Tag. You are calculating the tax using the expression:
[=F(TN('{PRICE}') * 0.0825),0.00] where 0.0825 is replace it with your tax rate %
When you made the Order Tag Group you chose to add the Order Tag Price to the Orders Price so it makes it Tax Included.
The constraint ensures its only applying it to those specific items.
It is adding the tax at item level using Order Added to Ticket.
The second Rule is recording the Transaction into Accounting by using the tag {ORDER TAG TOTAL:Sales Tax} Sales Tax is the name of your Order Tag Group that you made. This puts the total of those order tags into the transaction.
To sum it all up you are calculating the tax using an expression instead of a template and then recording it into the accounting you had setup for your taxes.
There are several benefits to doing this. Since you are doing taxes on Item Level you have more control. For example you could remove taxes from single item… etc
BTW I might add you may want to edit your printer Template so it excludes the Tax Order Tag from showing. To do this simply add this line to bottom of your template:
[ORDER TAGS:Sales Tax]
Sales Tax would be the name of the order tag group you made. This makes it so it will not show any Sales Tax order tags.