You start in Select mode.

To select items, click on them with the left mouse button.

To select multiple items, drag a box with the left mouse button.

If you drag from left to right, only items completely within the box are selected.

If you drag from right to left, all items withing the box are selected.

If you select with Ctrl pressd, then items can be added or removed from the selection.

To zoom the view, roll the middle wheel.

To rotate the view, drag with the middle button pressed.

To shift the view, press and hold Ctrl and drag with the middle button pressed.

Press the sphere button to create a sphere at x0 y0 z0, with a radius of 5mm

Press the cube button to create a 10x10x10 cube.

Press the cylinder button to create a cylinder based at x0 y0 z0, with a radius of 5mm and height of 10mm.

Press the cone button to create a cone based at x0 y0 z0, with lower radius 10mm, upper radius 5mm, and height 20mm

Draw some lines/arcs ( see below ), press the extrude button, enter the extrude height, in the Input window, and press the green tick.

Solids can be moved by dragging them, whilst in Select Mode.

When selected, gripper points appear. Dragging these perform other transformations, like scale, rotate, etc.

Press the Line/Arc button to enter line/arc drawing mode.

Click for the start point of a line and then for end points of each line.

Press and hold the 'A' key to switch to tangential arc drawing mode.

Press the circle button to enter circle drawing mode.

I think this is just for circle-through-three-points mode.

Press the infinite lines button.

Click on two points to define a line.

see the wiki page https://github.com/Heeks/heekscad/wiki/CoordinateSystems

Have a look at the "Options" window to see all the options.

When one object is selected, you can see its properties in the "Properties" window.

You can edit them too. Your changes can be cancelled by pressing the red cross button at the bottom of the "Properties" window.