At the top of the page, there is a tab that says Add...click on that and create a bulliten board for each major categories you want. When I first started, I created a board for Food, Decorating, Crafts, Style, and Just Because.
When I would browse through Pinterest and see things I liked, I clicked on Repin on that particular idea/recipe. A box should pop up that asks what board you wish to add it to. Click on the dropdown menu and choose the desired board.
Once you have pinned some things, click on your name at the top of the board. Under it, it lists boards. Click on that and it will show you all the boards you've created and the things you've pinned to each board. Its like an online file for all the neat things you want to keep up.
Hope this helps a little.