As you begin working on your projects, it is always good practice to save files often. Inkscape has a number of save options, in a number of formats, as well as ways to export into other common file formats.
By default, Inkscape typically saves files to your main documents folder. However, you are given an option to change this during the saving process each and every time you save a file.
By default, Inkscape files are saved as SVG files. The native Inkscape SVG format allows editing at a later time. If file size is a concern, you can also save in the Inkscape-compressed format of SVGZ and you will have no issues editing the file and resaving it for future use.
Inkscape can save as SVG, SVGZ, PDF, PostScript/EPS/EPSi, ...