Website traffic is the amount of visitors that come to your website. Usually they come slowly and gradually increase over time as bigger keywords make it to the top of search engines. If your company gets one order for every 100 visits to your website then you can quickly calculate the amount of revenue available if 1000 people visits your website.
Sometimes it's not the amount of traffic as much as the percentage of conversions. Conversion rates are a big term in the website world which is the number of phone calls or orders you get from each visit. That's where web design really helps the equation because less people buy from a lower quality website. However, getting more traffic through SEO services will also double or triple your chances as well. Once the visits start coming the design should be looked at based on how and when people back out of your website.
Analyzing what the visitors do on your website is the next thing to look at and possibly make changes based on data. If 100 people visit your site and all back out after seeing the home page then something is wrong. Possibly the design, images or content but information is gathered that something is going wrong. If 100 people visit your website and the navigate through the products and never buy anything there could also be problems. The point is that there's all kinds of data they we'll provide to you and you can analyze it and let us know if you want us to change something for you.