a. centre and radius:
Ribbon: Home > Draw > Circle drop-down > Center, Radius
Toolbar: Draw > Circle
Menu Bar: Draw > Circle
Command: CIRCLE or C
b. centre and diameter:
Drawing a Circle by Specifying Center and Diameter
1. Click Home > Draw > Circle > Center, Diameter on the ribbon. (or) Type CIRCLE or C in the Command line.
2. The following message appears in the command line.
Specify center point for circle or [3P/2P/Ttr (tan radius)]: Left-click with the mouse anywhere on the screen. (or) Type a Value.
Specify radius of circle or [Diameter]: Enter D for Diameter option.
Specify diameter of circle: Enter the value of Diameter.

The following prompts are displayed.
Specify first point
(i) Sets the starting point for the line.
(ii) Click a point location.
(iii) With object snaps or grid snap turned on, the points will be placed precisely.
(iv) You can also enter coordinates.
(v) If instead, you press Enter at the prompt, a new line starts from the endpoint of the most recently created line, polyline, or arc.
(vi) If the most recently created object is an arc, its endpoint defines the starting point of the line.
(viii) The line is tangent to the arc.
Specify next point
(i) Specifies the endpoint of the line segment.
(ii) You can also use polar and object snap tracking together with direct distance entry.

Close
Connects the first and last segments.

Undo
Removes the most recent segment of a line sequence.

LINE:
LINE Specify first point: Start point.
Specify next point or [Undo]: Position the cursor and then enter distance.
Specify next point or [Undo]: Position the cursor and then enter distance.
CIRCLE:
Drawing a Circle by Specifying Center and
Diameter
1. Click Home > Draw > Circle > Center, Radius on the ribbon.
2. Select an arbitrary point in the graphics window to specify the center point:
3. Type a value as the radius and press ENTER.
ERASE:
Method 1
Select the Erase command first and then select the objects to be erased.
Press Enter Key and the objects selected will disappear.
Method 2
Select the object to be erased.
Press the Delete Key.

(i) Click View tab Palettes panel Command Line.
(ii) Find. Press Ctrl + 9.
(iii) At the Command prompt, enter COMMANDLINE or COMMANDLINEHIDE.
(iv) L. It can be used for making simple lines in the drawing.
(v) C. It is the command used for making a circle in AutoCAD.
(vi) PL. This command can be used to make a Polyline in your drawing.
(vii) REC. This command will make a rectangle in AutoCAD.