Constructions in maths means you use pencil, pair of compasses and ruler. No measuring is used so the ruler is only for drawing straight lines, compass for circles. Oh of course an eraser for mistakes and that is why you pencil and not pen. So with this particular construction you need to know how to bisect an interval (part of a line).
You bisect each of the sides (these in fact are also the perpendicular bisectors) of the triangle and where the 3 p.bisectors meet is the centre of the circle you seek. if you then place the point of your compass on the point of intersection and open the compass to one of the vertices and using the same opening check for all three vertices you will see that they all have the same compass opening. Of course this will be true only if you have taken care with all of your constructions so that they are precise and accurate. These constructions are extremely accurate so any small deviation while performing them will mean that your accuracy will be compromised and the final result will be out.
Then draw your circle.
hope it helps