I have files, in Tiff format, downloaded from ASTER-GDEM.
Can I open this file with QGIS? If yes, how?
From your question, I'm assuming you are a new user of QGIS.
Tiff files are a type of Raster, which are supported in QGIS. The fact that your Tiff is a DEM (Digital Elevation Model) just gives meaning to the values of the pixels in the Raster, but does not affect the file format.
That all being said. Here is how to add a Raster (Tiff, in your case) in 2 easy steps.
Add Raster Layer
.tifffile, and press
Here is the result:
Since your raster is a DEM, there are a couple additional steps necessary to make it display properly.
Style Taband under Contrast enhancement, Change the Current pulldown from Default
No Stretch, to
Stretch to MinMax
Here is the end result with the DEM symbolized based on the raster values.
This process all being said and done, I would strongly recommend you to peruse the latest QGIS documentation: Version 1.8
As well, there is a wiki for QGIS that may be most helpful: How do I do that in QGIS?
It is likely that these two resources may lead you to an answer, as well as provide you with additional information.