You use it for cutting small irregular holes in wood
Obviously A router is NOT a saw. -To cut patterns use a jig saw or a scroll saw.
jig saw and a plastic bit or one with lots of teeath
A skill saw, table saw or jig saw work best.
A fretsaw, a jig saw, a sabre saw, a reciprocating saw or even a drill bit in a drill-press.
Yes, if you have the special blade to do so. I use Bosch or Lenox blades with 32 teeth per inch
a coping saw will cut tight corners internal and external. The blades are only 2 millimetres wide so are very flexible. A jig saw will also do this type of work and is easier to use because its machine driven.
a jig holds something in place so you can draw or do something on the object........
You will need a saw of some sort: A hand held Key hole saw will work, it will just take some time. Careful use of a large construction saw will do, but a single slip will cause big damage. A circular saw can work. Just be very careful.
Jig
Drill 4 large holes (3/8 -1/2) where you want the corners to be, then use a 'keyhole' hand saw to cut a line between each hole. (this is a small, cheap drywaller's saw that costs less than $10.
For speed, you would use a circular, or 'skilsaw' . You could also use a tablesaw, a mitre saw, a chopsaw, or even a reciprocating saw .
Sae 30 weight oil