How to draw line between two points using the mouse move in C#

You seem to be having a problem with what I'll loosely call a flag.

You need to tell you application when the mouse is first clicked and store its location.
Then, you need to tell your application when the mouse was clicked at the second location so you can call the line-drawing function.

At this point, what you want becomes unclear. Do you want to connect each new mouse click to the last one so you draw a series of lines connected to one another, or do you want to make new lines that are generally not connected to one another.

And that is where the flag comes in. You need to manage what your program's state is in. In the first case, all you'd need to do is keep track of the most recent click, and then, on a new click, draw the line and save the new point. In the latter case, you need to set a starting point, and then, when you click the ending point and draw the line, you need to clear the data. Or, have a flag that tells the system if it's waiting for the first or second click of the pair.

OK - now, use your debugger and see the state of your application as you step through it. Is the reason to draw more lines re-enabled? Or perhaps, you keep drawing the same line, over and over, making it look like nothings happening.

You will need to figure this out - and the learning will make you a better programmer.