Look in the wiiflow/settings folder for categories_v4.ini file. If not there then you may need to run wiiflow and access the categories menu once. Open it with wordpad or notepad+ and scroll down to the [GENERAL] section. This is where you set how many categories you want and the name of each category. Here is an example using the one made by BostonBC on GBATemp and included in Abz's all in one pak.
[GENERAL] cat1=Action cat10=Sports cat11=Strategy cat12=Traditional cat13=Theme cat14=ESRB: Early Childhood cat15=ESRB: Everyone cat16=ESRB: Everyone 10+ cat17=ESRB: Teen cat18=ESRB: Mature cat19=ESRB: Adults Only cat2=Adventure cat20=Hidden cat3=Fighting cat4=General cat5=Health cat6=Music cat7=Racing
cat8=Role Playing
cat9=Simulation
hidden_categories=4
numcategories=21
required_categories=
selected_categories=
The setup is cat#=name. replace # with the number of the category and replace name with the name of your category. Add as many as needed for the maximum number of categories you have set. Set numcategories to the number of categories you want plus 1.
Run wiiflow and select a game. Now press 'B' on the FAVORITES (STAR) button or go into SETTINGS and select CATEGORIES. Now you will see a page with the name of the game and all the categories below. If you have a lot of categories then use the PAGE button to go to the page the contains the category you want. Simply click on an empty box to add the game to that category or uncheck it to remove it from that category. When done selecting categories for your game you may press '+' or '-' to go to the next or previous game and select categories for it or press 'B' or the BACK button to go back.
OFF, ON, and HIDDEN are pretty obvious but REQUIRED is a bit tricky to understand. Here's an explanation of REQUIRED. Hope it helps.
Example:
game1 in cat1
game2 in cat2
game3 in cat1 and cat2
if you set cat1 and cat2 to checkmarks (ON) wiiflow will show all three games.
if you set cat1 and cat2 to + (REQUIRED) then only game3 will be shown since it's the only one in both cat1 and cat2. Note: setting only one category to REQUIRED cancels out all other selected (ON) categories. REQUIRED is for selecting two or more categories.
Run wiiflow and from the main screen press 'B' on the FAVORITES (STAR) button. Now you will see the CATEGORIES MENU. Here you can choose what categories to see or hide. Only games in those categories selected will be shown or hidden when you return to the main screen. If you have a lot of categories you will need to use the PAGE button to go to the page containing the category you want. Each category has four states - OFF, ON, REQUIRED, and HIDDEN. Keep clicking a box to cycle through the four choices. If you wish to go back to all games then simply click the CLEAR button to deselect all categories. When done simply press 'B' or the BACK button to go back and see what you've done.
You can use the CATEGORIES MENU to hide games. Name a category to "Hidden" and set it to X (HIDDEN) and all games you place in this category will not show. If you have PARENTAL LOCK on then all categories set to HIDDEN can not be changed until they are unlocked by going to SETTINGS MENU and entering the correct password/code.