In most cases, you will need to write a cover letter to highlight your skills and achievements. The only times you don't need to upload a cover letter are when: (1) You can't (i.e. you can't upload it to your application); or (2) the company specifically states you shouldn't.
The question is: how do you write one?
1. Start by introducing yourself.
The goal of your cover letter is to introduce yourself and show potential employers what you have to offer. Naturally, you should start off your cover letter with a short introduction.
2. State how your specific experiences and achievements can help the firm.
You want the job, so you have to state how your experiences can benefit your target company. Write down what the company needs and tell them how you can satisfy that need. For example, "As a content marketer, I can handle your social media accounts and boost your follower count through..."
3. Write the closing paragraph.
Here is where you will ask your potential employer to refer to your resume and get in touch if they have any questions. You can thank the potential employer for his or her time, but make sure you don't write things along the lines of, "I look forward to speaking to you soon," as it sounds arrogant and presumptuous.
4. Sign the letter.
Sign the letter with something like "Sincerely/Respectfully yours," your name, and your signature. If you're sending your cover letter through email, then you can also add your contact number, Skype address, or other relevant contact information under your name.
5. Note the other documents you've enclosed.
Whether you are sending your cover letter through snail mail or email, make sure your resume is attached. If you're sending it through email, you can mention in your closing paragraph that you have attached your resume to the email. If you're sending it through snail mail, then a few lines after your signature, write "Encl: resume."
Things to keep in mind:
- KISS: Keep it Short and Simple
- Personalize: Talk about the job post or company a little bit so that the firm knows that you have done your research.
- Proofread: Make sure there are no typos or grammar errors—those will never look good on a cover letter and might even hurt your chances of getting the job.
Good luck with the job hunt!