A variety of wood species are actually sold as teak, but real teak, also known as tectona wood, is a tree native to Southeast Asia. Many suppliers sell wood called teak from Brazil, which is a different (but similar) species known as cumaru. The cumaru woods are plantation-grown, and are often used for flooring. Conversely, tectona is typically harvested from native forests, as the tree can grow as tall as 120-feet and live to 100 years.
Because the tectona variety is harvested using clear-cutting methods in Southeast Asia (primarily in Myanmar and Indonesia), a lot of environmentally-conscious consumers have issues with the use of teak for woodworking projects. This is quite different from the cumaru varieties that are essentially farmed in central and South America, much like pine plantations are planted, harvested and re-planted in the United States and Canada.
Because of the differences in varieties of hardwoods sold as "teak," there are considerable variations in color of the raw wood. Some teak may be a rich chestnut color, whereas other boards may appear to be almost yellow in color. As such, when building a project, try to buy all of the wood you'll need from the same lot at the same supplier all at once so that you have a consistency of color across the project.
Working with Teak:
That being said, gluing up teak boards isn't as simple as other hardwoods or softwoods. The heartwood of teak trees (of both the tectona and cumaru varieties) include a resin that is extremely water resistant. As such, the benefits that teak provide for outdoor woodworking projects can actually make it more difficult to glue the boards together.
The way to handle this is to wipe down all surfaces of the joint with acetone or denatured alcohol (much like working with ipe) using a clean rag. Allow the acetone or alcohol to dry completely before applying glue to the joint and clamping the joint together.
A more traditional (and dare I say, appropriate) approach to finishing teak is to clean the wood and then apply a liberal coat of teak oil to all exposed surfaces. Allow the teak oil to soak into the wood as much as you can before wiping off the excess and allowing it to dry for a couple of days before exposing it to the elements.
Refinishing oiled teak involves a three-step process: clean the surface using a spray cleaner with a non-abrasive pad, then clean off any additional residue and resins with acetone or denatured alcohol, and finally an additional finish coat of teak oil. Depending on your environment, you may have to clean and refinish your project as much as every couple of years to keep it in pristine condition.