It is complicated But first you want to do one of two things
Either do a bedrock or java model (I don't know the diffference)
Or do a skin model (Basically you chose what ever mob you want and you can reskin it)
If you choose bedrock or a java model you then have to make it but first you need to know the tools (They are on the top of the screen)
The move tool: It is the one with the three connected arrows on it, Just click the block you want to move then pull the arrow in the direction that you want it to move
The Resize tool: It is the one with the four arrows on it, Just click the block you want to resize then move the flat arrows in the direction you want it to be resized in
The rotate tool: It is the one with the two arrows going in a circle, There is a panel with all the sizes and you would want to center the pivot point then just rotate the block with the arrows
I don't know how to use the rest but these are the most important ones
There is also a panel in the lower right corner that has all the blocks and to add more click the plus button to add a new block and enable more options
You might also want to create folders and add certain blocks into it that go together (Right click the folder and rename it to head or body then add the blocks into it by dragging the ones you want in them)
The two options you want to use are the lock and eye
The lock disables you from accidentally moving, resizing, rotating or painting the block by accident and the eye makes the block visible or invisible
Then when you finish making the model of your mob, you should then go to the textures panel in the lower left corner and click add texture then a pop up should appear then enable template then when you click ok ignore the next pop up and click ok then go to paint choose colors and paint the model (Use the visibility button which is the eye to disable certain blocks so you can paint the whole block easier)
And there is the paintbrush button and eraser button that you can change the size of the brush and the opacity of the color
And there is a bucket tool that paints the whole face by default but you can change it to paint the whole cube, all the colors that are on that face that are the same or all connected colors that are the same
Then save the project with the file button at the very top of the screen then you can load the model and texture anytime in blockbench to edit it or take a screen shot
There is also a animate tab with the edit and paint tab but I don't know how to use it
