Using a graphics tablet and pen with Adobe's Illustrator vector graphics software makes the process of drawing lines and shapes more intuitive and realistic. For added control over the software, turn on the pen pressure setting in Illustrator. When pen pressure is on, Illustrator changes the brush based on how hard you push on the tablet. If you set the pen pressure to affect the brush diameter, for example, pushing firmly on the tablet with the pen causes the brush's diameter to expand. You must have a pressure-sensitive graphics tablet connected to your computer before you can enable this option.
Connect your graphics tablet to your computer. Launch Illustrator.
Click the brushes icon in the right-hand toolbar to open the Brushes palette window. Double-click the brush you want to use to open its options window.
Click the "Diameter" drop-down menu and click "Pressure." Click the "Angle" and "Roundness" drop-down menus, and click "Pressure" for each, if desired.
Click "OK" to close the options window and turn on pen pressure in Illustrator.
You must enable pen pressure individually for every brush you want to use. If Illustrator doesn't allow you to turn on the pen pressure option, ensure that your graphics tablet is connected and that you've installed all the necessary drivers. Adjust the Variation setting to control the degree to which the pen pressure affects the brush.