How to select all points within a circle in PostGIS?

I have set of points in a PostGIS Table (Type Geometry).

Now, I need to filter points that lie in a circle with a center (C) and radius (R)!

I expect C to be of type Point or Coordinates.. R to be in Meters!

SELECT * FROM my_points
    WHERE ST_Within(point, ...)

However, I don't know how to complete it..

How can I exactly measure C and R?

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