The best way to advertise is to have something people want to buy and a very clear one-line value proposition on how it will change someone's life for the better. Building a Story Brand is one of the most approachable and easily implementable books on creating marketing content, with great examples, and even a step-by-step guide to your home page.
Generally, beyond that, most "free" marketing actually means that you put effort into it. For example, content marketing where you gather a library of helpful resources that attract people, and occasionally advertise your product/service along with it. u/bawlerblog posted a comment in this thread where the offer free content marketing advice (For tech related niches). Even if that's not your niche, there will probably be other people offering a free content-marketing strategy session who are hoping to sell their services that way.
The other thing people do is create a free download to attract people who will sign up to your email list (and who you can then advertise to). The easiest way to create this is to create a free guide/tool/step-by-step exercise PDF that will make someone else's life easier. This adds an extra step in advertising, but it has the benefit of allowing you to offer something for free rather than immediately asking for something.
I'd create a brand messaging framework to reflect back to and re-wireframe your website with new copy. If you can't hire a conversion copywriter + designer, I highly recommend reading Building a StoryBrand. I work in this field and it's totally worth the investment of time and/or money–whichever you prefer. I use this method and so far, all but 1 of my marketing clients made their money back within the first 2 months. Copy is powerful!
Given that I am trying to bring the audience to speed quickly on something they would unfamiliar with, I would apply the principles outlined by something like Story Brand.
In the ad I would want to:
Identify how this product addresses a felt need, enables the person to achieve an aspirational perspective of themselves, concluding how your company could guide them and how your product accomplishes that goal. I think of the way apple interacted with the budding portable music player market.
I know this is years late but I thought I'd reply for the future people who might so happen to stumble upon this thread.
Building a brand a starting a business are two separate things. A business is a legal entity that sells goods or services and a brand is a business with emotional assets that connect with it's audience and customers.
When you ask how to build a brand, you're really asking how to create a brand strategy. Here are resources to help you to do exactly that:
My biggest piece of advice is to get really clear about your why aka purpose.
Check out Muse Storytelling, or their courses at Muse University. They have a great breakdown of developing a story, even in commercial work.
Another good resource is the book Building a Story Brand. Even if you’re not in any sort of advertising, I have found the principles of that book really helpful in thinking about story.