The drawing tools in Photoshop let you create vector shapes with different attributes. Lines are such an essential element of design that Photoshop includes a drawing tool expressly designed for making lines. Using the Line tool, you can choose the weight and color for your line by adjusting the tool's options, then quickly draw lines at any angle. When you draw multiple lines, Photoshop creates different shape layers, so you can edit each line independently.
Press the "U" key to select the drawing tools, then hold down "Shift" and press "U" to cycle through the tools until you enable the Line tool. Alternatively, click on the visible Shape tool, and then click on the Line tool icon in the Options bar.
Enter a pixel value into the "Weight" box for the line in the Options bar to set its thickness.
Click on the color swatch in the Options bar and choose the color for the line from the color picker. Click "OK."
Click and drag with the tool in the document window to draw a line. Release the mouse when you finish drawing.
Hold down the “Shift” key to keep the line perfectly straight. Double-click the line’s layer thumbnail to open the color picker and change the color of the line at any time.