I installed QGIS, GRASS and GDAL by OSGeo4w package, and as I finish the installation, I want to use GRASS tool, I face this problem：
But I already installed GRASS and SAGA, how to make those tools in QGIS to be used？
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You need to configure the GRASS and SAGA folders in QGIS. Follow these instructions from the QGIS documentation on Configuring external applications:
The processing framework can be extended using additional applications. Currently, SAGA, GRASS, OTB (Orfeo Toolbox) and R are supported, along with some other command-line applications that provide spatial data analysis functionalities. Algorithms relying on an external application are managed by their own algorithm provider.