How to use: http://info.sonicretro.org/SCHG_How-to:Set_Up_SonLVL

Controls:
Up, Down, Left, Right: Move the camera by 16 pixels.
Hold Shift: Move the camera by the size of a chunk (usually 256 or 128 pixels).
Hold Ctrl: Move the camera to the edge of the level.
Ctrl+O: Open
Ctrl+S: Save
Ctrl+Z: Undo
Ctrl+Y: Redo
Alt+Enter: Enable/Disable fullscreen mode.
F5: Show/Hide the menu.
Ctrl+Tab: Switch to next tab.
Ctrl+Shift+Tab: Switch to previous tab.
Ctrl+1: Switch to Objects tab.
Ctrl+2: Switch to Foreground tab.
Ctrl+3: Switch to Background tab.
Ctrl+4: Switch to Art tab.
Q: Disable collision viewing.
W: View collision path 1.
E: View collision path 2.
R: Toggle viewing of angle values.
T: Toggle objects above/below high plane.
Y: Toggle viewing of low plane.
U: Toggle viewing of high plane.
I: Toggle grid.
O: Toggle HUD.
P: Toggle viewing of objects from all timezones (Sonic CD only).
[: View previous palette.
]: View next palette.
-: Zoom out.
+: Zoom in.

Object Editing:
Left click: Select an object or ring group. Hold Ctrl to select multiple objects.
Left click empty area, drag: Select all objects within an area.
Left click object, drag: Move object(s).
Double left click: Create a new object.
Shift + Double left click: Create a new ring group.
Ctrl + Double left click: Create a new special bumper. (Casino Night only)
Right click: Bring up a context menu.
Delete: Delete all selected objects.
Numpad 12346789: Move selected objects by grid size in direction of number.
A: Decrease type of all selected objects. (no undo)
Z: Increase type of all selected objects. (no undo)
S: Decrease subtype of all selected objects. (no undo)
X: Increase subtype of all selected objects. (no undo)
J: Increase grid size.
M: Decrease grid size.
Ctrl+X: Cut selected objects.
Ctrl+C: Copy selected objects.
Ctrl+V: Paste copied objects.
Use the property grid on the right to edit the selected object(s)/ring group(s).

Level Editing:
Left click: Draw with the selected chunk.
In Sonic 1 mode: Double click to toggle the loop flag.
Right click: Select the chunk under the cursor.
Right click, drag: Select an area.
Right click inside selected area: Open context menu.
A: Decrease index of selected chunk.
Z: Increase index of selected chunk.
Use the list on the right to select a chunk.

Chunk Editing:
Click and drag chunks in the chunk list to re-order them, hold Ctrl to swap two chunks.
On the chunk preview:
Page Up, Page Down, Home, End: Change current chunk.
Up, Down, Left, Right: Change selected chunk block.
X: Flip horizontally.
Y: Flip vertically.
S: Increment solidity.
Shift+S: Decrement solidity.
T: Increment secondary solidity (S2/S3K chunks only).
Shift+T: Decrement secondary solidity (S2/S3K chunks only).
B: Increment block index.
Shift+B: Decrement block index.

Block Editing:
Click and drag blocks in the block list to re-order them, hold Ctrl to swap two blocks.
On the block preview:
Page Up, Page Down, Home, End: Change current block.
Up, Down, Left, Right: Change selected block tile.
X: Flip horizontally.
Y: Flip vertically.
P: Toggle priority.
C: Increment palette.
Shift+C: Decrement palette.
T: Increment tile index.
Shift+T: Decrement tile index.

Tile Editing:
Click and drag tiles in the tile list to re-order them, hold Ctrl to swap two tiles.