What John is talking about is SEO or search engine optimization. Besides giving someone your web address personally there are two main ways of driving traffic, or hits. SEO or SEM, search engine marketing.
Most of the 3 majors, Google, Bing, and yahoo, work the same way, for our discussion I am going to focus on Google. SEO affects your 'search rank' or where you show up on the page for a given search term, or keyword (tree service, tree removal, ne pennsylvania tree service etc.) SEO is something that can be done in the creation phase of web design, building your site so it indexes correctly, and is viewed by the search engines correctly and efficiently. SEO ranking also extends into inbound links, which is other sites linked to yours based on other keywords etc. You can pay for links or get them from other industry partners, news stories, blogs etc. (even the house).
An internet marketing firm or SEO firm can execute a plan that attacks these and other options for increasing your page rank. Ultimately you want to show up on the first page of Google for your given keywords. (tree service, tree removal, ne pennsylvania tree service etc.)
SEM is another story. When you search Pennsylvania Tree service
http://www.google.com/search?client=safari&rls=en&q=Pennsylvania+Tree+service&ie=UTF-8&oe=UTF-8 You see these ads
Local Tree Services | ServiceMagic.com
www.servicemagic.com/
Find Locally Rated Tree Services. Get Free Estimates. Visit Us Today!
1,179 people +1'd ServiceMagic
Local Tree Services | yellowpages.com
www.yellowpages.com/
Find Area Tree Services & Arborists Removal, Cutting, Tree Care.
or sponsored links. This is PPC or pay per click marketing, when a user searches a given keyword, Google shows them ads that have that keyword indexed to it. The advertiser, you, doesnt pay anything for me to see the ad, only if I click it. Click costs range between $.05 all the way up to $50+ for "mesothilioma" and related terms. "Car insurance" falls somewhere around $5. I would imagine "tree service" or related terms are $.05-$.20 / click. If you look into it Google Adwords has all sorts of resources availiable
http://www.google.com/ads/adwords2/
Setup is free and you can easily put budget restraints of as little as you like. Weekly, daily and monthly limits are availiable, they will help you select keywords based on your business and there are actually classes you can take for free online to learn more about managing your own adwords acct. Customers can actually be 'chosen' on many factors including zip code, city, and all sorts of stuff.
You can pay a SEM/SEO firm to manage all this for you or you can do it yourself.
My advice would be to make an investment in proper SEO, which if done right should last and hold value. You can update it as things change but good SEO at first is a cornerstone as John mentioned. Follow it up with self managed SEM using adwords. Dont pay someone to manage it, try it yourself and if you are overwhelmed look into a firm.
Here is a resource for Adwords professionals, you can easily take the free courses and become an expert yourself
http://www.google.com/adwords/professionals/individual.html
If you want to really track your advertising sources look into call tracking
www.mongoosemetrics.com
Orange Soda is well respected SEO/SEM Firm
http://www.orangesoda.com
There is obviously room for you in the local SEM market. NO OTHER tree services showed up for "PA tree service" I would imagine that with the location based searches you would likely be the top sponsored link with correct bidding at a reasonable cost.
Remember, all the SEO & SEM in the world wont do you any good if people get to your site and leave. You need to capture them, then their info, drive a call, ask for a web submission...
Whoever you go with for design or seo/sem, If they dont talk the talk and seem passionate, find someone else.
Look at other tree services sites, be prepared with specific examples, links or printouts of both what you like and dont like. Ask family, family, friends, women, and people that are not tree guys. Tree guys dont hire other tree guys so our opinions of your site might not reflect the customer base.
I honestly believe that there is a huge market for SEM/adwords in our business. Most markets are devoid of it, I have done a bit of research, and most people wouldnt think of doing anything other than searching 'pittsburgh tree removal' or 'cleveland tree service'. Go for it.