7D space is divided to 4 main and 3 secondary dimensions. Seven large cubes are the sides of the cube directed to main dimensions, and they are arranged as faces of 4D cube. Each face is 6D cube and it's represented as a Cartesian product of two 3D cubes - that is cube (in main dimensions) built of smaller cubes (in secondary dimensions).
Sides of smaller cubes (we call them "blocks") are directed in secondary dimensions. Note that orientation of all blocks is the same, so stickers of 7C cubie are not collected around the corner of the face: some of them are on other corners of the corner block. Small stickers that attached to sides of blocks actually belong to "secondary" sides of the cube. So we can see all stickers of cubies on main sides, but only some stickers on secondary sides. It means, for example, that we don't see colors of centers of secondary sides of 3^7. But it's not the problem - centers of main sides are deep inside the cloud of cubes, so we almost can't see their color too.
The first thing is the navigation in 3D image of the cube. Left button of mouse can be used to rotate the image, right button (or ctrl-left button) - to zoom in and out, shift-left button - to change the direction of view (sometimes it's called "pan").
Right-click of the sticker highlights other stickers of its cubie - but only visible stickers. Sometimes you can see more than 7 of them (up to 16), it's because secondary stickers may be shown more than once: each of them appears at every visible main sticker of the cubie. To reject highlighting just click somewhere in empty space.
By checkboxes in the right panel you can hide pieces with the selected number of visible sides (1C, 2C, ...). Three-state checkboxes under the color buttons are for the selective highlighting of stickers: if some box is checked then the corresponding color must be in the highlighted piece, and if it's empty, then the color can't be in the piece. To turn this highlighting on and off use checkbox "Highlight by colors".
Twisting is implemented in 2-click way: first you select face and one of its 2C centers, and then select "target" center. It's difficult to find 2C cubies in the image, so there are some more ways for selection.
If you want twist main face from main direction to another main direction, click any large sticker of 2C block of the face. Then click any large sticker of the face in the target direction, or any large sticker of the 2C block of the twisting face that is directed to the target direction. If target direction is secondary, second click should go to any small sticker in that direction. To twist main face from the secondary direction you may make first click either in sticker of 2C cubie (it's inside the side - center of some face of the central block), or in the center of face of any not-2C block of the twisting side. Second click goes as it the first case.
To twist the secondary face from the main direction click the small sticker of any cubie that has only one small sticker (it is at the center of face of some block). Second click should go to any sticker of the target face - main or secondary.
To twist the secondary face from the secondary direction find some cubie that has exactly two small stickers. One of them should belong to the twisting face and another be directed in the start direction.
If you are not sure have you made first click or not, click in the empty space. Next click will be considered as the first click of the twist.
If this 2-click mode is difficult for you, try 3-click mode. You click the face that you want to twist (be careful: small stickers belong to secondary faces!), then the face in direction "from", and then the face in direction "to".
In the status line you may see progress bar "status of clicks". If progress bar is on 25% or 100%, program is ready for the first click, 50% means that face is selected, 75% - that first direction is selected. Red color indicates that last click was wrong, and program waits for good click (or for click in the empty space - it works as "cancel".
If you want to twist internal layer of the cube, press a key with the number of the layer (2,3,4...) or several keys (to turn more than one layer) during the first click of the twist.
To see other sides of the cube use ctrl-click. There are 1-click and 2/3-click commands: if the first click is made not in large sticker of the central side, then the side containing this sticker goes to the central position. If you click sticker of the central side then you want to keep it in center but change two other sides (probably to switch between main and secondary ). It works in the same way as the main side twisting and requires two (or three) clicks.
You can save useful sequencies of moves as macros. Ctrl-M starts macro. First you must select the sequence of reference stickers (program continues to ask them while the set is symmetric). Then make some twists, press Ctrl-M again and enter macro name. It will appear in the listbox in the right panel.
To start macro, left-click its name, select "Apply" or "Reverse" command and select sequence of stickers (if it doesn't match the reference sequence, background becomes red).
If you click in the empty space during sticker selection, it cancels macro definition or application. To cancel macro defenition after sticker selection, press Ctrl-M and click "Cancel" button.
Macros file can be saved and loaded.
If you make some twists before your favorite twists sequence (or before macro) and want to make them in reverse after that, do the following.
If you make [F1 A F2 B F4] sequence (where A and B are some twists sequences) it will be equivalent to [A B inv(A) inv(B)].
Blocks F1..F2 may be nested or delayed. For example, [F1 A F1 B F2 C F1 D F2 E F4 G F3 H F2 K F3] is equivalent to [A B C D E inv(D) inv(E) G inv(B) H K inv(A B C D E inv(D) inv(E) G inv(B) H)] :)
If you press F3 when the last block was not closed (i.e. [F1 A F3]) then F1 will be canceled. Also if you press F2 when the last block was closed but not applied, you "unblock" it. Last string in the right panel shows current state of the stack of blocks.
Other features are usual: Undo/Redo; Open/Save log file, Scramble (1-5 twists or "full"). Also you can select another puzzles - from 3^4 to 5^7.