Hello Mal,
Thanks for asking. 
Yes, please add following CSS under X > Theme Options > CSS to have 2 column layout on checkout page:
@media only screen and (min-width: 900px) {
.woocommerce-checkout #customer_details {
float: left;
width: 50%;
}
.woocommerce-checkout #order_review_heading {
float: left;
margin-left: 3%;
}
.woocommerce-checkout #order_review {
float: left;
width: 47%;
margin-left: 3%;
}
.woocommerce-checkout form {
width: 90%;
margin: 0 auto;
}
}
Please let us know how it goes. In case above CSS give some issues, please share your website URL for us to take a closer look.
If you would like to learn CSS, I am sharing few resources that you take a look to get started with CSS and an interesting tool that you can use to speed up the development process.
I recommend you to watch following video that will help you to get started with CSS.
https://www.youtube.com/watch?v=MFR4WXiLzpc
Sometimes it can get a bit difficult to find out the right selector to be able to write the required CSS codes. A handy tool that can help you in this is Google Chrome dev tools. I am sharing the resource that you can refer to get started with dev tools.
https://developers.google.com/web/tools/chrome-devtools/css/
https://developers.google.com/web/tools/chrome-devtools/
https://www.youtube.com/watch?v=tP_kXBJWPhQ&t=200s
Thanks.