Using a Router

Dear friends
Im looking to purchase a New Router... Admittingly I have never used one so Im anxious to learn ...
For instance when cutting out a profile for a tear how do I set it up for use in cutting with the router so it gets cut nicely as I have drawn it...
Do I build an edge to follow or? do I set the template on the ply as usual and then use the edge to cut?
Classic Finn
Im looking to purchase a New Router... Admittingly I have never used one so Im anxious to learn ...
For instance when cutting out a profile for a tear how do I set it up for use in cutting with the router so it gets cut nicely as I have drawn it...
Do I build an edge to follow or? do I set the template on the ply as usual and then use the edge to cut?
Classic Finn