There are widget areas that can be viewed under the Appearance > one sidebar areas with 2 custom widgets (Author and Latest News).
Rinjani Author Widget
Describe who you are in the sidebar with this widget.
Latest Post With Thumb
This widget will show your post with the thumbnail at the sidebar.
To use this theme you need to activate Mailchimp for WordPress plugin in require plugins. After that follow the instruction from Mailchimp to get API key. Then insert this HTML markup in Mailchimp > form:
<label>Enter your email address below to subscribe to our newsletter.</label>
<input type="email" name="EMAIL" placeholder="Your email address" required />
<input type="submit" value="Sign up" />
After make a form, go to appearance > widget > and drag the Newsletter widget into sidebar area to activate it.
Add an advertisment image with 125px size and link it to another site.