If you are looking for layout customizations beyond the Style & Typography settings built into the theme, it’s important to judge the nature of customization.
If it’s a simple layout change, it’s very likely achievable by using Custom CSS. However, for something not possible using either of these, a child theme is recommended.
WPBeginner has a great article on How to create a WordPress Child Theme. Use
Template: kutir instead of twentyeleven.
@import url("../kutir/style.css"); in the CSS file to import parent stylesheet.