Your marketing agency's job is to deliver leads to your sales team. That's what marketing is. Marketing is doing what it takes to deliver leads. This is different from sales. The job of a sales person is to close deals. The job of a marketer is to start them.
Your brand is what articulate's organization's identity. It is the aggregate of fonts, colors, messages and everything else that tells the story of your organization. Having a brand and taking an active roll in defining your brand is a way to deliberately define how the world sees your organization.
Creating a brand is not the same thing as marketing. A good brand will make it easier for the marketing team to generate leads. If the brand is well defined, well positioned, visually clear and intelligent it will be easier to build a meaningful relationship with your market. Good branding makes it easier for your market to identify with your organization, and makes it more likely that your target market will want to identify with your market. However, good branding does not generate leads. Generating leads is not branding's job. Branding's job is to tell a clear and consistent story that defines the organization. Branding's job is not to create leads. Marketing's job is to create leads.
Public relations gives your organization an active roll in defining how media outlets identify your brand. Often, public relations is the field that insures THAT the media notices your brand and brings it to the attention of your market. It is a combination of telling your organization's story and making the effort to get your organization's story told in a way that your market will hear it.
Public relations is not responsible for generating leads. Public relations can make it easier to generate leads by making your company more familiar and more trusted by your market. But it's job is not to create leads. Marketing's job is to create leads.
This is probably the most important part of this article. Search engine optimization (SEO for short) is also not marketing or lead generation. SEO's job is to make the company's website as authoritative, noticeable and well trafficked as possible. This is often described as "Getting to #1 on Google".
SEO is not marketing either. That is crucial for organization's to understand. A great SEO can direct a company how to get more traffic and better ranks for the terms the market values. But in truth, SEO cannot create leads either. SEO brings the market to the website, but it does not convert the market into a lead. That is marketing's job. That is specifically the job of inbound marketing.
Inbound marketing is a way to use your website, social media, SEO, paid ads, PR, branding, and email to create leads. It is a way to use the internet to create a lead generating machine for your organization.
An inbound marketing campaign is centered around generating leads that a sales team can close. It focuses all of company's efforts into getting the traffic to the website that will develop a positive view of the brand and convert into a lead that the sales team can close. Often an inbound marketing campaign will center on something which a visitor can download if she will give her name, email address and a few identifying factors that let the sales team know if she is a good prospect.
If your agency is focused on branding, it is a design agency. If it is focused on PR, it is a public relations agency. If it focused exclusively on SEO, it is an SEO agency. All of these services are necessary to most (all?) modern businesses. But for most businesses, all of these services are really just a means to an end: lead generation.
If lead generation is the real ROI of engaging an agency, it should be clearly defined as the center of everything the agency is doing. Create your inbound marketing strategy first, then build your brand, your PR, and your SEO around it.