Jevelin theme has three predefined widget locations where you can place your widgets.
To access widgets go to Appearance > Widgets. From there you can add widgets by clicking on them and choosing the right location.

Here is the full list of available widget areas:

• Blog Widgets – for blog pages and blog posts
• Page Widgets – for standard pages
• WooCommerce Widgets – for WooCommerce pages
• Portfolio Widgets – for portfolio project pages
• Footer Widgets – for footer