how to get a job in designing field?

Every and any company may hire a designer with little to no experience. The position may not pay well, and you may not have the title of "designer", but you'll have a place to start.
To improve your skills, you need to know how to create parts. There are many aspects of design though, so you may need to narrow down the scope of what you wish to work on. A good place to start may be a company that produces prototype parts, you'll see a wide range of designs and projects in such a shop.
Some designers are very imaginative and come up with wonderful and beautiful designs. Other designers create more practical designs that can be manufactured and sold for a reasonable cost. You'll need to decide if you'll create imaginary objects, or if you will create objects which can be fabricated.
I think your best options for applying will be to create a proper resume which highlights your skill with various design and related software/skills. You'll also need a portfolio showing products, parts and designs you have created. Then you can hand deliver this package to various companies in your area (also don't forget the obvious things, like dressing well, combing your hair, shaving...etc.). If you are willing to move, mail the package to other companies in the areas you'd be willing to move to.
Do not focus on companies that have a "now hiring" sign. Just go to the companies you wish to work at, meet with them, shake hands, take a tour, show them your work, fill out an application, see what happens!