Alpa, before you proceed you need to familiarize yourself with Upwork. There's a wealth of information within the Help and Support area as well as within this Community. All one needs to do is search for what they want to know, read/view, absorb it, and put it into practice. We do appreciate helping others that help themselves.
re: "I want to help to write proposal to get my first job. I know that you all are very experts in this field and I'm sure I will get help."
Don't be so sure.
Nobody here is going to help you write your first proposal.
To do so would be a disservice to you. We would be hindering your progress. Therefore, we're going to leave this as something you need to study out for yourself.
Study, study, study. The Community Forum has hundreds of posts about how to write proposals and how to get your first job.
As you research how Upwork works, you'll find the basic process to being hired on new projects here is:
1) Use the "Find Work" function from the main menu to screen for available projects that suit your experience and capabilities in your field of expertise and appear to meet your requirements for compensation
2) Apply to each project via Upwork with a cover letter that clearly describes to each potential client how you can solve their problem/fulfill their needs, attaching any documents, work samples, etc. that support your claims of expertise and experience. Be as specific as possible in each application to show that you understand the client's requirements, but don't hesitate to ask questions, especially ones that will reflect you know what you are doing and can help them define as well as solve their specific problem(s)
3) Be very quick to communicate with potential clients to answer any questions they have about you, your experience, etc.
Starting out on Upwork you'll have a very steep learning curve and, depending on your area of expertise, a lot of competition. Persistence will be your best friend.