Hello, everyone,

Right now I am going to introduce you the most fundamental, and also the most important function in AutoCAD: Line.

First and foremost, I would like to introduce the most basic command, Line. We click on this Line icon in the tools panel.

Then, we can click at different points on the blank surface with our cursor,

and lines will be formed. In AutoCAD, every line can be edited.

You may also draw several lines continuously, and formed a series of joined lines.

When we click to select these lines with our cursor, each line can be edited independently.

Let us try clicking it, after you select a line, there will be three blue points on it.

Among the three, the ones at the two ends, the starting and the ending points, they are for adjusting the length of the line;

While the point at the centre, that is for moving the line around.

Now, I am going to introduce you the Line command for drawing this red square on the right hand side.

It is 100 units times 100 units.

Before that, I want to first introduce you a function called the Dynamic Input

Here at the bottom right corner, you will see the icon for "Customization", when you move your cursor over there and click on it,

a menu will be shown,

and you can select "Dynamic Input".

So, you will be able find this function in the menu, or down here, there is a small icon for "Dynamic Input"

Turn it on, please. Then, we will be able to use Dynamic Input as we draw this square.

After we turn on the function of Dynamic Input, we click the Line icon.

As we are drawing, we will notice that, there are a lot of information appeared next to the cursor

Here you can see the information about the length, the angle, even this "Specify next point or" such hints for your reference.

Now, I am going to demonstrate how to use relative coordinates to draw this square.

First, select our first point, the top left point of the square. Then, we give relative coordinate for the second point of the square.

That will be (100, 0). Why? Because we are going 100 units to the right and no units to either up or down, so it is (100, 0)

The third point that we are going to add, we are moving downwards 100 units.

So what is the relative coordinate? (0, -100), so that is what we should key in.

This will mean move downwards 100 units. The next point is quite simple, it's moving to the left.

And how do we do that? The relative coordinate is (-100, 0). This is the coordinate of the forth point as related to the third point.

So, the relative coordinate for the forth point is (-100, 0).

Another command to know is when you change your mind about what to key in. You may find that, 'Ah, this point is wrong!'

Then, what do you do? This is a very essential command in AutoCAD, called the command "U",

that is, "Undo", so, to undo what you have just key in, type "U"

So you go back to the previous step, and we can do it again.

Okay, let us put the lines back, (-100, 0) (0, -100)...

Lastly, I would like to add, from the second last point to the last point, that is, when you are going to close this square,

In AutoCAD, we use the command "C", it stands for close.

So, we use C, close and you closed this square.

Of course, you can also choose to use the relative coordinate to close this square,

But usually, we use the command "C", to make sure that the diagram we draw here is a closed diagram, that the lines are indeed connected.

Next, I am going to show you how to draw with polar coordinates. Here we have designed an irregular quadrilateral.

You see here on the right, there is an irregular quadrilateral ABCD.

AB us a horizontal length of 80 units, BC has an angle of 80 degrees,

and a length of 80 units. While CD has an angle of 85 degrees and the length is 60 units.

and there is no length and degree given for DA,

because we can simply use command "C" to close this closed polygon.

So, how do we draw this irregular quadrilateral ABCD?

Well, we need to learn about polar coordinates first. Polar coordinates is when you give a length and an angle,

you should be able to plot the ending point of a line.

So here, what we need to pay attention to is the angle. The angle is calculated starting from the X-axis, going in the anti-clockwise direction.

So, let me demonstrate how to draw this ABCD with polar coordinates. 。

First, we plot point A,

After we selected point A, as we move to point B, we input 80, that is the length of this relative polar coordinate,

and we key in the angle 180 degrees, because this line and the X-axis formed an angle of 180 degrees.

From point B to C, length is again 80, this is simple. Then, what's the angle? between this line and X-axis, the angle is 80

Then, from C to D, no problem with the length, 60.

It is the angle that may cause some problems. It is slightly difficult, we have an angle of 345 degrees between the line and the X-axis.

Of course, you may also key in -15, that will be the same as 345 degrees. So this is how polar coordinates work.

Lastly, after we got point D, to reach point A, we simple key in command "C", close,

and we are able to get line DA. Well, use polar coordinates,

we can complete this quadrilateral ABCD