cos and sin expect a value in degree and return a value based on the unit circle (so they return [-1,+1])
To position something on a circle around a center:
x = center_X + cos(angle) * radius
y = center_Y + sin(angle) * radius
To move something circular around a center over time:
angle = angle + amountofchangepersecond * TimeDelta
x = center_X + cos(angle) * radius
y = center_Y + sin(angle) * radius
You may also change angle and/or radius independently for x and y which will have various effects, like shaping an ellipse instead of a circle and much more.