Open Paint. If you need to, extend the white workspace by clicking the bottom right corner and dragging toward the lower right.
Create the panels first. Select the "Rectangle" tool on the toolbar to the left. Click and drag the rectangle for the first panel. Click the "Select" tool and click and drag your mouse to cover the entire rectangle. Select "Ctrl" + "C" and then "Ctrl" + "V" (or select "Edit" --> "Copy" and then "Edit" --> "Paste"). Click the copy of the rectangle and drag it to the right until it is lined up with the first panel. Make the "Paste" command again and drag over the third rectangle to match up with the other two.
Draw your comic inside the first square by selecting the shapes at the right. If you are making a person, use the circle command for the head, eyes, body and maybe the hands and feet. If you are comfortable using the mouse to sketch your characters and scene, click the "Pencil" button and draw it yourself. Continue to draw your comic throughout the strip.
Add color by selecting the "Fill With Color" icon. Select a color at the top of the screen and click any closed object inside your comic to fill it with color.
Add text to your strip by selecting the "Text" icon. Click and drag the text box where you'd like it and type in your text.