To add a slider on a theme you will need to access the file where you want to add a slider and use the code below:
<?php echo do_shortcode( '[ irideslider id=xxx ]' ); ?>
Replace the xxx with the number of the slider you want leaving no spaces between the squared brackets.
To add sliders to posts and pages you will find an extra icons for Iride Slider on WordPress editor.
Clicking on that icon a slider selector will open. Click on the slider you want to add to your post and the shortcode will be created automatically.
To add a slider to a widget area go to WordPress widgets under the Appearance menu. There you will find the Iride Slider widget where you can select the slider to use.