Hello Mandar,
Even though, there are many problems, congratulation on finishing your first challenge, we all start somewhere.
Now, I won't go through everything, but rather, I'll give you a good path to start completing those challenges correctly.
First of all, you definitely need to learn display: flex, and display: grid. Those are more than crucial to web development, and are probably used in 100% of website. So, head over to YouTube and learn those well and how to implement them efficiently. You can learn from Kevin Powell, Web Dev Simplified, or even from full HTML/CSS tutorial with projects. All those are useful.
For rounded corners, when you have an image, and a container, you need to apply border-radius on both of those elements, so both of them have rounded corners with the same value.
To make responsive design to multiple devices, you need to learn about media queries: @media. Same story, head over to YouTube and learn those.
When you start challenges like this, at least for me, I look at the main-container first, and organize the layout. So for this challenge, there is one main-container, and that container is divided in two parts, the image, and the information. Then I would decide which type of display to use, for this one I used grid. Then, I would look at the sub-containers, mostly for the information, and how to structure them to fit the design. For this challenge, for the information, I put all the information in a container with display: flex and styled it to the design.
Anyway, to first start a challenge, you need to know how to break it apart, and then analyze what CSS properties you would need to reassemble it. It sounds hard, but with experience and those simplified design, a quick glance and you can know what you will use.
I hope you understood what I explained, if not, please write a reply, otherwise, I wish you a great day:).