To extract features from the Satellite image there are mainly two steps:

i. Creating False Color Composite of multiband Image

ii. Digitizing features using vectors

i. Creating False Color Composite of multiband Image

If one is using Landsat data, then each image would have different bands in the form of tiif file (.tif).

1. Add all the bands of Image in QGIS

2. Now, merge multiple bands into a single raster. For this purpose, In main menu go to Raster-> Miscellaneous-> Build Virtual Raster. Build Virtual Raster window appears.

In the window in Input Layers, select all the bands. You can leave other parameters as default. Specify the output and then press run. Your image is added as a layer.

3. Right click on your image under the layers and go to properties->Symbology. The render should be Multiband.

For the Red band use Band 5

For the Green band use Band 4

For the Blue band use Band 3

Click ok.

ii. Digitizing features using vectors

With the help of visual image interpretation techniques identify different features in your image.

Now in the main menu go to View-> Toolbars. Select Digitizing and Advanced Digitizing toolbox.

In the main menu, go to Layer->New Layer. You can use New Shapefile layer if you want to digitize only one feature.

For multiple features in one file, you can use New Spatialite layer.

Give name to your layer, select type of your layer, specify CRS same as your raster CRS, specify attributes and click ok.

For creating features, select the layer you want to edit. Go to digitizing-> Toggle editing. And a pencil would appear with the name of layer you are editing.Click on add features tool in digitization toolbox. After drawing the feature, right click to stop drawing. A pop-up would appear, give value to attributes, click ok. Click on save layer edits to save your edits.