My first tip for most people would be to start with the Part Design workbench, although if you're coming from OpenSCAD, you might prefer the Part workbench. FreeCAD has many different workbenches for handling various use cases, such as architectural models, surface trimeshes, 2D machine shop drawings, and so on. The various workbenches do mostly work together well, but for a beginner it's intimidating to have so many options.
"Part Design" is probably the most familiar approach for people coming from high-end CAD programs like SolidWorks; it uses the 2D sketch + extrude workflow. The similarly-named Part workbench is for people who prefer to think in terms of boolean operations on solids, which is generally the OpenSCAD way.
https://hackspace.raspberrypi.com/books/freecad
(last time I printed it, I had to add a blank to get things to duplex right)
I make some pretty basic things to 3d print with FreeCAD and everything I've learned came from YouTube.
Typically for me it just new part, new spreadsheet, part design, sketch with dimensions parameterized from spreadsheet. Pad or some other boolean of solids, repeat starting at new sketch.