QUESTION 1
When a tangent to a circle intersects the circle's radius, the angle formed is a right angle.
This is based on the Circle Theorems: "The angle between a tangent and a radius is 90°.
QUESTION 2
A tangent to a circle is a straight line that touches the circle at only one point.
Consider the image below:
If two segments from the same exterior point are tangent to a circle, then they are congruent. This means that for the image above, we have that:

QUESTION 3
The basic difference between a secant and a tangent is that in a secant, the line intersects the circle at two points. But a tangent intersects the circle at only one point around its outer line.