This article will show you how to store the data of multiple checkboxes as a comma-separated list inside Memberstack. This other article can show you how to set up a single checkbox.
Here's a link to clone the project seen in the video.
Create a Wrapper Element
Somewhere inside of a profile or signup form, you'll need to add a div. And then, you'll need to give that div an attribute of
data-ms-member="ID" where the ID points to a custom field inside your Memberstack account.
Add your Checkboxes
Next, you'll want to add all of our checkboxes inside of the wrapper element. For this to work, each checkbox's input is going to need a
data-ms-value="VALUE" attribute where the value is what you want to be saved in Memberstack.