Question

what is the construction of tangent

Answer 1

It is a line from the center to the given point P on the circle. By construction, SP is the perpendicular to OR at P. SeeConstructing a perpendicular to a line at a point for method and proof. The tangent line is at right angles to the radius at the point of contact. See Tangent line definition

Answer 2

It means that construction of a line to a circle that touches the circle at exactly one point, never entering the circle's interior.