Question

please explain circumcentre of triangle

Answer 1

It is the mid point of the e triangle which is at equal distance from all the vertices

Answer 2

The circumcentre of a triangle is considered to be the point of intersection of the perpendicular bisectors of the sides of a triangle. 
In other words we can say that circumcenter of a triangle is the point where perpendicular bisectors of sides of a triangle intersect each other.