Each sentence ends with a punctuation mark like a period.

Sentences in a professional document like a cover letter should almost always end with a period, not a question mark or exclamation point.

There are no commas separating complete sentences.

"I would be a good fit for this position, I have good communication skills." is incorrect.

Instead, use a connecting word like or, and, but, because, or so. For example, "I would be a good fit for this position because I have good communication skills."

If a connecting word doesn't work very well, you may be able to turn the sentence into two separate sentences.