Typing: Reports, survey documents, population statistics, etc all have to be entered into the computer preferably in a data base format or as tabular data.
Scanning: Paper maps such as USGS Topographic maps, aerial photographs, remotely sensed images if not already in a digital format need to be scanned and then georeferenced or georectified. When a picture or a map or an aeiral photo is georeferenced it will open in a GIS program in the right place on a map in relation to other map objects being viewed. They will be in the proper place spatially.
It's also possible to scan a written report if OCR software is available to translate the image into a word or database type document.
Digitizing: Maps can also be digitized if more than just a photograph of an existing map is desired. Digitizing is basically tracing points, lines, or areas from a paper map, or aerial photo so that instead of a photograph or a raster image, instead there is now a digital line graphic or vector file.
GPS data capture: Data can also be placed in a GIS as points, lines, and polygons from a GPS unit if it has the capability of recording such information.