Well, I thought the README file (look under Calling sequence:) did that.
&tft is a pointer to (& means address of) an Adafruit TFTLCD object (created when you instantiated the 2.8" TFTLCD display library)
&ts is a pointer to an Adafruit TouchScreen object (created when you instantiated the 2.8" TFTLCD TouchScreen Library)
XP, XM, YP, and YM are the pin numbers for X+,X-, Y+, and Y-, respectively. The same arguments had to be passed to the TouchScreen library, so, you should have them relatively handy.
X and Y are the X and Y coordinates on the display of the upper left corner of the virtual button.
W and H are the Width and Height (in pixels) of the virtual button.
Note that X and Y (and W and H) include the area of the button used for beveling, specifically a 3-pixel wide border, so you should draw the button from X+3,Y+3 to (X+W-4, Y+H-4). Otherwise, part of your image will get overwritten by the beveling process.
C is the background color for the button. This is used in the beveling algorithm. Usually it will be the output of tft.Color565(r,g,b).
M is optional. If you specify it, it will set the button mode of operation. You can use B_Name.setMode() at any time to change the mode. If you don't specify a mode here or with setMode, then it defaults to ONESHOT.
If that doesn't give you what you need, then send me a PM and I'll try to help you.