in mahjong sanctuary, how do you use the bookmark power up?

I agree it would be helpful to have better information on more than a few Pogo games:

Mahjong Sanctuary (MS) “bookmarks” are not for saving games so you can quit the game, come back later and retake where you left off.

If you quit, you lose all progress.

What this power-up does is put a “bookmark” on the last good match of your choice, and this way--while you are in-game--you can always go back to where you set the bookmark and retake your game from that specific point.  This is useful when you might need to go back on the moves you've made in the game (when you get stuck) and want to try a different “path” or strategy -- without having to use multiple “Undo” power-ups.

In my experience, the most useful MS power-ups is the “egg” for an extra slot -- the “shuffle” -- the “joker” to select a tile which removes it and all similar tiles from the board - and just a handful of the “Show Pairs” which is especially helpful during the dust storms because available matches will shine through the murkiest storm like Batman’s signal--or the brightest flashlight..

TIP:  During storms, bright red letters in the right hand box will show how long--or how many moves Player must match--before the storm covering the board moves on and off--that’s really the most ideal time when the “Show Pairs” is best utilized.

PRO TIP:   Before you start MS, always make sure to look on right hand side and see how many Available Matches there are. 

It’s important that if you think you will forget, make a quick note.  Why?  Because if you should lose that game and hit “Back to Sanctuary” and then “Play,” you most likely will see a decrease in available matches.

Save your time and sanity:  when that happens, just hit “Back to Sanctuary” and “Play” as many times as it will take to get the same or more available matches as the first game board you played. Make note if it is more Available Matches than the first game in case you lose again.  Good Luck.