Not much to add to the explanations so far. Patterns in general are a great way to make use of expert knowledge (that is solution blueprints for often occuring problems). It's definitely worth it to get familiar with at least the main design patterns.
Another good page which explains the basic patterns very well is:
http://sourcemaking.com/[
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If you're in an ASP.NET environment i would forward you to the MS Application Archhitecture Guide. It epxplains the main architecture types (not only 3- Tier) very well in my opinion. It also includes plenty of links to HowTo's for specific tasks in ASP.NET and many more stuff.
http://msdn.microsoft.com/en-us/library/ff650706.aspx[
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