LeoCAD is Hard to use initially. Here are some tips I've figured out.
View - Rotate and Pan
Right mouse drag to rotate the view.
Click the globe in top right corner of workspace to quickly change the view to Front perspective, Left, Right, etc., or in-between. You may drag the globe too.
ALT + middle mouse drag to pan the view. This is troublesome if you're using a tablet or touchpad with no middle mouse button! - so do the next bullet to save your day.
Open 'Tools' toolbar to get the 'Pan' mode button, by right clicking toolbar area and check-select 'Tools'.
Click the Pan 'hand' button to enter panning mode - left drag to pan view.
Click the Select 'arrow' button to return to normal.
Sometimes a submodel's axes could be in a weird orientation, making it hard to pan and rotate with respect to the main model. In this case, use menu command 'Edit> Transform> Absolute Transforms' (enable it, instead of 'Relative Transform) to change the axis back to global axes orientation for easier panning and rotation.
Finding Parts
This is a nightmare initially! Learn to use the 'Search Parts' search box.
On a big screen, drag to enlarge the parts panel to show more parts at once.
If you're recreating Lego build instructions or looking for a specific part (especially anything not a simple brick, plate or beam) from a set. Try this:
Turn to the last pages of your Lego build instructions manual to find the part number. Type this in 'Search Parts' box and hope the part shows up.
Remember to switch back to 'All Parts' especially if nothing shows up.
Though it's not uncommon to have no results.
Download the build instructions from either:
Lego @ https://www.lego.com/en-sg/service/buildinginstructions/
Or fan recreated LDDs @ EuroBricks forum
If no result, Google "Lego <part number>" like "Lego 4294180" to find the name of the part. Type an unique word from the part name in 'Search Parts' box. Hopefully you get a smaller list of parts from which to find the one you want.
Search quirks:
Spaces needed when specifying part size: like 2 x 8 and not 2x8.
Spaces not needed if using my Enhanced LeoCAD.
Remember common terms like 'without corner', 'curve', etc. The search phrase must be an exact match anywhere in the part name.
If using my Enhanced LeoCAD, matching is looser. The search phrase is broken up into separate keywords (space delimited) and all parts containing all the keywords are returned.
If you've used the part before, copy/clone it from that LDR file. PS: .LDR is the file extension for LeoCAD outputs, wheres Lego Digital Designer files are .LDD
If the part is part of a group, the entire group is copied!
Miscellaneous
To change colour of existing part in build:
Select the new colour in palette.
Select the parts in build.
Select menu command: Piece > Paint Selected
Use and create submodels.
Especially create entire blocks in submodel, then add them back to main project to be rotated.
Export submodels to separate LDR files for reuse or editing.
Use Timeline to organize the build steps, to help other users build your set IRL.
To move part(s) to another step:
Select the part(s).
Right-click the step to move to, and select 'Move Selection Here'.
Advanced Tips - Text Edit LDR
Sometimes it's way easier to edit the LDR by text instead!
Open LDR file in text editor to copy and paste parts easily - if you can handle text!
Rearranging steps is easier too!
'0 STEP' line indicates start of new step.
Refer to this ldraw page for details of LDR file format.
Bulk delete empty steps (i.e. consecutive lines of 0 STEP \n 0 STEP) easily.
To change a part in place:
Select the part to be replaced in LeoCAD and get its part number in status bar. E.g.: Brick 10 x 10 ... (ID: 58846.dat) means the part number is 58846.
Mouse-over a replacement part to see its part number.
Search and replace the numbers in LDR. QED.
Can also copy and paste entire LDR contents as submodels into another LDR, and vice versa.
Also useful for reorganizing existing builds: move groups of bricks to new submodels.