There are ready-to-use binary packages available for most of the platforms supported.
After installation, you can immediately start working with SAGA. Simply execute the file saga_gui (saga_gui.exe on windows). The first thing you should verify is that the SAGA module libraries got loaded. In case they were not, you can load the module libraries by choosing Load Module Library from the Modules main menu. You will find the libraries in the subfolder modules of your SAGA installation path.
If you have raster data in different formats than SAGA's own grid format, use one of the Import modules to import the data. Shapefiles and tab-delimited tables can be loaded directly. An easy way to play with SAGA is to download one of the demo datasets. Load the data and double-click on the datasets in the Workspace window to display them in a map view. Use the navigation tools to zoom and pan (zooming out is achieved by right-clicking). The section First Steps provides examples based on demo datasets. To get a clue on how to use the modules you may like to take a look at the page Using SAGA Modules. A list of documentation on SAGA (e.g. the SAGA User Guide) can be found on http://www.saga-gis.org, section References.
Download the ZIP of the latest SAGA MS Windows binary release (saga_version_bin_mswvc.zip) and extract all files to a directory of your choice. Alternatively you can download the installer saga_version_setup.exe and execute the file.
64bit binary packages and recent development snapshots from cvs can be downloaded from http://www.laserdata.at/saga_packages.html.
There are binary packages available for some Linux distributions to use with your package manager and a tar you can try with others.
Debian and Ubuntu linux Debian includes a version of SAGA GIS meant to be part of the next release (squeeze): http://packages.debian.org/en/saga Backports for Debian lenny (i386 and amd64) are available here: http://zadeh.ugent.be/~johan/saga/lenny/
SAGA GIS is available on launchpad for users of Ubuntu hardy(8.04) up to maverick (10.10). After adding the right archive, you can install saga using the standard ubuntu tools. More information is given on this page: https://launchpad.net/~johanvdw/+archive/saga-gis or if you are in a hurry you can run:
sudo add-apt-repository ppa:johanvdw/saga-gis sudo apt-get install saga
Other linux distributions Download the GZ of the latest SAGA Linux binary release (saga_version_bin_linux.tar.gz). Extract all files to a directory of your choice. To run SAGA you first have to copy SAGA's API library libsaga_api.so to a location that is listed in the LD_LIBRARY_PATH environment variable. Copy the library into one of the standard directories (e.g. /usr/lib) and run ldconfig (or /sbin/ldconfig depending on your linux distribution). If you can't or don't want to install the library in a standard place (e.g. you don't have the rights to modify /usr/lib), then you might want to add the library's location to the LD_LIBRARY_PATH environment variable, e.g.:
$ export LD_LIBRARY_PATH=/usr/local/saga_2.0:$LD_LIBRARY_PATH
Now find the file saga_gui and execute it (make sure the executable flag is set, otherwise chmod +x will do so).
In case you encounter problems, assure that you have the following libraries installed (you may use your package manager to do so):
You can search for unresolved dependencies by running ldd on libsaga_api.so.
To install the latest native FreeBSD binary from internet simply do as superuser
pkg_add -r saga
The next part you only need to read if you want to download the native binary of SAGA manually for some reason. Then you have to differentiate between FreeBSD OS versions and platforms to choose the right path.
To download SAGA for example for FreeBSD 10.0-CURRENT on amd64 platform you can use ftp://ftp.freebsd.org/pub/FreeBSD/ports/amd64/packages-10-current/Latest/saga.tbz and on i386 platform you can use ftp://ftp.freebsd.org/pub/FreeBSD/ports/i386/packages-10-current/Latest/saga.tbz.
For other OS versions you have to substitute packages-10-current with one of the following strings: packages-8-stable, packages-8.4-release, packages-9-stable, packages-9.1-release, packages-9.2-release.
Note, that not every binary version is available all the time. That depends on periodically runs of the FreeBSD package build cluster.
Once you have downloaded the right SAGA tarball, the following should do the installation:
pkg_add -r saga-2.1.0.tbz
Last note: On FreeBSD it is not guaranteed that there is a binary tarball for every version at every time. In case you do not find the right one, you should consider to build SAGA GIS on your own, see Compiling SAGA from sources on FreeBSD.