FreeCAD is a parametric CAD program. A Sketch is a type of thing within FreeCAD. Sketches are defined using constraints and dimensions, not free-hand drawing.

Blender is polygon-based 3D modelling with (pretty much) free-hand drawing and no constraints or dimensions.

FreeCAD and Blender can both export to many of the same formats (notably STL, for 3d printing), but their internal data representation, and supported workflow, is completely different.

FreeCAD is more appropriate when you want mechanical parts, and Blender is more appropriate when you want something artistic like a figurine.

CAD is operated based on constraint, e.g. make a square box and say "I want this to be 30mm x 45mm with this point, add a fillet (rounded corner) then make it coincident with this point" and let the software figure out how to shape/position the object. While Blender is more of a free-hand drawing, e.g. make a square box, make it certain size, make a corner rounded, then move it to the a certain point.

Blender has ability to do simple constraint, but it's not its primary uses. FreeCAD can also be used the Blender way but the software will warn about being under-constraint. Both FreeCAD and Blender can export to STL file (used by CAD softwares), but Blender's STL usually need to be scaled to real world measurements. In case of 3D printing, this STL file can be imported into a slicer software such as PrusaSlicer, which outputs GCode to control the printer (e.g. X, Y, Z coordinates, extrusion temperature, etc.)