To draw an ellipse from a center point, use the Ellipse tool. Indicate the center and then the end of one axis of the ellipse to determine the angle of the ellipse. Use the third indication to determine the length of the other axis of the ellipse.

Ellipses and elliptical arcs (trimmed/partial ellipses) can be difficult to properly constrain and dimension. One very important thing to remember regarding this is that you can use the Parallel constraint with them. This will set the major axis parallel to a line or another ellipse. If you do not want the line in your sketch, you can put it in a separate 'construction' sketch. Also, dimensioning or constraining the center point and using the min and max radius dimensions are useful techniques for ellipses.

Finally, tangent constraints are also useful. You can even create a rectangle (by 3 points so it can be at an angle) in a 'construction' sketch; make the ellipse parallel to a long side of the rectangle; and then make the ellipse tangent to each of the sides.