Writing a thank you letter for a scholarship is good etiquette, just as writing a thank you when receiving a gift.
If the letter is being sent as a hard copy, then it should be in the proper business format, otherwise, if the letter is being emailed, it should have an appropriate subject line and proper grammar.
I would like to take this opportunity to thank your organization for awarding me the [Scholarship Name] scholarship for [Time Frame of Scholarship Benefit]. It is truly a great honor to be selected as a recipient of this award. This scholarship will help greatly in reducing my financial burdens and allow me to focus on my education
I [am/will be] attending [School Name] and [am/plan on] majoring in [Major]. Upon successful completion of my degree, I plan on pursuing a career as a [Desired Position].
[Include any other pertinent information such as your financial struggles, your passion for your area of study, or your future aspirations]
Thanks again for investing in my future, I will make sure to do my best in achieving my academic and career goals.