My problem is not exactly related to my résumé, but I am having problems when it comes to my cover letter. I don't know what it should include or how to correctly send one. So what should a cover letter include? Also, I usually sent my resume via email because that's the way they want to receive it, but should I send it as a PDF or a .doc?
See my suggestions and share your own in the comments! Just
Cover letters are typically your résumé's counterpart and are sent at the same time. You can simply make your cover letter the body of the email while attaching the résumé (unless the job listing specifically asks for no attachments). When I say that the letter is a résumé's counterpart, I do not mean that it should duplicate the information you've already included in your resume, rather that it should serve as a less formal complement to it.
Review the qualifications listed on the job description, and pair them against your résumé to generate examples of how qualified you are for the position. Consider the cover letter an opportunity to showcase more about you and what you're capable of than what can be conveyed through your résumé.
Focusing on yourself is the easy part, but you must blend in plenty about the company to show that you want to work for them and aren't just looking for any old job. You want your own attributes to make you stand out, but highlighting how interested you are in their company can only help you. Demonstrate your knowledge about the type of work they do , their clientele, why you want to work there, and be enthusiastic (but not obnoxiously so).
At all costs, avoid addressing your cover letter with "To Whom It May Concern." It's stuffy and shows that you didn't take the extra step to find the appropriate name. Make sure that your cover letter is written well, showcases your personality, won't make the reader fall asleep from boredom, and most of all, makes you stand out more than you would have if you'd never written the letter.
As for how to attach your résumé, Word documents are widely used and likely compatible with most computers, but PDFs allow you to submit a résumé that cannot be altered. I've always submitted my résumé as Word documents — how about all of you?