These examples and descriptions of publication types will give you an idea of how to use various works and why you would want to write a particular kind of paper.
Scholarly article -- example
By writing a scholarly article you are contributing to a community of thought on a particular topic. A scholarly article allows you to communicate your research with your peers. It should provide complete information about a particular piece of research. Frequently, publishing a scholarly article is a time-intensive process. The highest caliber journals are generally peer-reviewed, and getting your research reviewed can take a while. To get your research out to the world faster, try publishing a conference article!
The key to finding scholarly articles is using scholarly databases or browsing scholarly journals.
Conference paper -- example
A conference article is similar to a scholarly article insofar as it is academic. Naturally, you need to find a conference appropriate to your subject area where you can present the paper. One great thing about conference articles is that they are published more quickly than scholarly articles. You can get your research to your community much faster via conferences than journals. Many conference publications are peer-reviewed, especially in computer science. You can find conference papers in many of the same places as scholarly articles.
Note: the button doesn't always work for conferences!
Review article -- example
A review article summarizes a particular field of study and places the recent research in context. It provides an overview and is an excellent introduction to a subject area. The references used in a review article are helpful as they lead to more in-depth research. You might want to write a review article to summarize progress in a field you've been working on.
There are several ways to search for a review article. Try using Inspec and selecting "general review" from the "all treatment types" drop down menu. In many databases you can simply type "review" into the title. This isn't always effective, however, as such a search retrieves extraneous information and misses a lot of relevant material. Other keywords you can use to search for a review article include: survey, overview, summary, etc. Some journals, like the Foundations and Trends series as well as Morgan and Claypool's Synthesis product, are devoted entirely to review articles.
Letter -- example
A letter is shorter than a scholarly article and does not present a full explanation of research the way a scholarly article does. It is usually an explanation of work that has been done, either a design or research, without all the data presented. You would write a letter if you just wanted to summarize your work in a brief document without presenting all your research. Letters are often used to get the word out quickly about research, and then followed up by complete journal articles. Many journals are devoted to letters alone, for example: IEEE Computer Architecture Letters and Electronic Letters on Computer Vision and Image Analysis.
Design paper/specification -- example
A design paper is a detailed description of a design that you plan to make or have made. It consists of an overview of what others have done and where your design fits in, a plan, and an explanation of technical requirements and solutions.
Searching for a design article can be tricky. They aren't labelled as "design articles," so it's nearly impossible to search just for them. However, in Inspec, if you limit your search to "practical" under "treatment" you'll be guaranteed to get some design papers.
White paper -- example
A white paper is a document that falls somewhere between a brochure and a manual. You can write a white paper if you want to provide a general, technical explanation of an architecture, framework or product technology. Companies provide white papers to help users and researchers understand and use their products.
To search for a white paper, try Google and a company web site.