QGIS, or Quantum GIS, is an open source GIS application framework: QGIS distribution is mainly a map viewer and editor, enhanced by numerous plugins.
QGIS upstream is a GitHub repo. QGIS hosts its own poorly organized official site, which has a Redmine issue tracker and lists all QGIS plugins.
Graphic Interface: main menu, toolbars (modes, measure, edit, import), status bar, dialogs; canvas.
Advanced digitizing panel; Tracing (base layer);
Spatial bookmark: save and name a viewport.
Expression: wildcard: %, used together with LIKE.
† denotes customized shortcuts.
?, keyboard shortcuts†
F12, options (preferences)†;
C⇧p, project properties;
p, pan map†;
s, select features†;
i, identify features†;
e, edit (toggle;)†
a, add feature†;
m, move feature†;
n, node editor†;
t, tracing (toggle);
-, zoom out†;
+, zoom in by rectangle†;
1, zoom to data (full);
2, zoom to layer;
3, zoom to selection;
8, previous viewport;
9, next viewport;
0, zoom to native resolution;
PgUp, zoom in;
PgDn, zoom out;
Cb, add bookmark;
C⇧b, show bookmarks;
F5, refresh;
Ch, hide selected layers†;
C⇧h, hide all layers;
Cu, show selected layers†;
C⇧u, show all layers;
Ca, select all features in selected layers;
C⇧a, deselect all features;
Ms, select by expression;
Cf, filter by expression;
Ct, attribute table†;
Ci, insert/update attribute (field calculator)†;
C⇧m, measure line;
C⇧j, measure area;
Cr, raster calculator;
CMp, Python console;
Processing:
CMc, options;
CMd, commander;
CMh, history;
CMt, toolbox;
QGIS is much less powerful than GRASS GIS, you may read this discussion about the differences between QGIS and GRASS.
QGIS ships with a GRASS plugin, acting as a more friendly interface of GRASS.
QGIS OSM support is in menu (Vector > OpenStreetMap), which can download and import OSM files by geometry type and with selected tags via a SpatiaLite database connection. OSM's 64-bit identifier is supported in QGIS.
QuickOSM plugin can send Overpass queries from QGIS to get OSM data.