Advertising has 2 meanings.

Insiders typically mean “paid media” when they mention advertising, e.g. “how much advertising (”ad”) budget do they have?”, but most people think of advertising as the marketing industry in general.

An advertising agency, often referred to as a creative agency or ad agency, is a business that specializes in creating, planning, and managing advertising and marketing campaigns for clients. Here's a brief overview of what advertising agencies do:

Creative Campaigns: Advertising agencies develop creative concepts and ideas for advertisements across various media platforms, including TV, radio, print, digital, and social media.

Market Research: They conduct market research to understand the target audience, consumer behavior, and industry trends. This information helps in crafting effective advertising strategies.

Media Planning and Buying: Agencies strategize where and when to place advertisements to reach the intended audience. They negotiate with media outlets to secure ad space or airtime.

Content Creation: Agencies create ad content, including visuals, copywriting, videos, and graphics. They ensure that the content aligns with the brand's message and objectives.

Campaign Management: Ad agencies oversee the execution of advertising campaigns, monitor their performance, and make adjustments to optimize results.

Client Services: They maintain close relationships with clients, ensuring that the client's goals and objectives are met throughout the campaign.

Digital Expertise: In the modern era, agencies often specialize in digital advertising, including online ads, social media marketing, and search engine optimization.

Measurement and Analytics: Agencies use data and analytics to evaluate the effectiveness of advertising campaigns, providing clients with insights and ROI analysis.
In Seattle, there are roughly one billion advertising agencies and you can find a list of top agencies through various resources such as Clutch, Expertise, and DesignRush. You should also talk to CROWN of course.

Remember, the specific services and expertise of advertising agencies can vary, so you should choose an agency based on their unique needs and goals.

See also: Advertising Design