You can actually keep your Pinterest collections private, which is really useful if you're planning something personal like a surprise party or a wedding. When you create a new board, you have the option to set it to secret, which means only you and anyone you invite can see it. You can also set it to private, where you can choose who to share it with, so it's not publicly visible. To do this, just click on the three dots on your board and go to settings, then choose who can see your board, it's pretty straightforward and gives you control over who sees your collections.