Some people are still having problems, hopefully whats below will help.
To tell the H2Hhelper where your game is just click on the 'Installs' button at the top of the H2Hhelper, then 'Add install' and you will get a box called 'Installations Details Dialog' with 3 fields in it.
The 1st is the game name 'CMBN'.
The 2nd is the install directory with a browse button beside it. Click on the browse button and a window comes up. In that window find where your 'Combat Mission Battle for Normandy' folder is, and highlight it and then click 'OK'. That will have told your H2Hhelper where your CMBN is.
The 3rd is for 'Dropbox location' with a browse button, click on the browse button and locate your Dropbox folder and highlight it and then click 'OK'. Then click 'OK' to get out that 'Installations Details Dialog'.
You might have to also tell it which Dropbox shared folder to look in for each game. To do that highlight the battle e.g. 'JohnsyvsRT' then click on the 'Game' button at the top of the H2Hhelper, then click 'Edit Game' A box will come up called 'Games Details Dialog' with 3 fields in it.
The 1st is the 'Game Name' e.g. 'JohnsyvsRT'
The 2nd is the 'Game File Folder' with a browse button next to it. Click on the browse button and in the window that comes up find the shared dropbox folder that will be used by both people to exchange turns and highlight it e.g. 'Johnsy Vs RT' and click 'OK'.
Don't worry about the 3rd field you shouldn't need it. Click 'OK' to get out of the 'Game Details Dialog' box. All should work fine then.
Make sure you have the 'Tidy' and 'Auto update' ticked in the 'Options'.