nickblender

The units snapped depends on the displaying grid. Therefore, we need to adjust the size of units displayed in grid. That can be done by going to 1) Viewport Overlay, and 2) change the scale Increase the size if you want smaller snapping, and larger size if you want bigger snapping

Goal: to  Step 1: Select the object that you want to extend Step 2: Go to Edit Mode (1), click 'Face Mode', click on the face on the object that the object is going to be extruded to. Step 3: Click 'G' key, and move downwards to scale downwards.

Goal: Subtract the mesh from this protrusion. Step 1: Extrude from the surface. Step 2: Select the faces of the protrusion: Step 3: Hit Shift + D, then hit Esc, then hit 'P'. The purpose is to create an object in the Outliner. This object, which is known as the cutter object, will be used for later step. Step 4: Adjust the size by hitting 'S', then hit the key by the coordinate you want to adjust to. In my case, it's 'Y'. You would also need to adjust the size of the cutter object downwards, as to make sure the boolean creates an internal cavity within the main object. How to scale in one direction. Step 5:  1) Select the duplicated object (cutter object), 2) add the Solidify modifier on the duplicated object. 3) Adjust the thickness (make sure that it's not too big, or else it will look like Figure 1.  The purpose of this is because we want to correctly subtract the solid volume. If this step is skipped, the boolean will only subtract the cutter's s...

How to extrude? 1) Click on an object 2) Go to Edit Mode 3) Select 'Face Mode' right here, then, click on the surface where you want to extrude the object from. Alternatively, you can press Ctrl + 3 to select 'Face Mode'. 4) Press 'E' to extrude.  How to reduce the size of the extruded object? 1) Select the face you want to extrude from 2) Press 'E', then press 'S' 3) Press 'E'