The first half of your sentence is correct
La TVA est incluse car =
VAT is included because...
Prestation usually is a
service rendered by a company (without context, I can't be sure it is so in your car

)
S'agir de can take various meanings in France, usually it is
"it is about...". In your case, it means
what we're talking about. So you can translate
il s'agit d'une prestation en France into
this service is rendered in France or
the service we're talking about is sold in France
or something similar.