A few Points that we need to consider while creating a cover letter are highlighted below.

Some Samples would always help you to get this done but please make sure what HR requires through their JD and other details. Spending 5 minutes more to provide exactly what HR needs, helps you get a call from the HR team.

Same Cover letter won't help to get a call always, try to experiment more than one way. 

1. Is a cover letter important while submitting a resume?
Yes, it gives the HR team to screen your skills and experience.

2. In which case should I add a cover letter?
- While Applying for a Job as a fresher and Experienced.
- While Applying for an Internship at a company.

3. What will be the size of a cover letter?
It should be around 200 - 400 words, But we prefer to make it short and crisp as per the Job description. Generic details for a cover letter are quite okay but if needed try to make changes.

4. What will be the structure of the cover letter?
There are so many different templates for that and nothing is standardized term. But we need to highlight skills with is relatable to the job description. A lot of people just add their resume without any proper subject body and cover letter which leads the email into the trash.
So it's important to add
- Personal Information 
- Experience 
- Skills 
- Why are you applying for a Job
- Your achievements 
- If there is a gap between previous employment, good place to highlight it here 
- For the Internship, you can mention college and college learning journey.