It’s always a good idea to use a cover letter in any job application. The cover letter is an important part of meeting the job description and ensuring that you’re able to discuss what’s in your resume. Just be sure not to repeat exactly what is featured on your resume. If you’re not used to writing cover letters, then you can use the ResumeHelp cover letter builder to craft a professional cover letter.
You should aim for about half a page to 3/4 of a page. This is long enough to impress the hiring manager with your highlights but it’s not so short that you seem unqualified.
If you’re applying for an entry-level sales position, then you just need to show that you have knowledge through other experiences. You can emphasize your soft skills such as your verbal and written communication abilities, for example, or talk about related experiences such as an internship or volunteer job in which you dealt with sales or customer relations. Either way, you’re still emphasizing certain experiences and skills that will qualify you for the new job role, even if you’re drawing them from a different place.