You can upload almost any list of potential participants into Pool, but there are some important steps to prep your CSV you want to take. One especially complex issue is handling multi-select data, which is when you have a questions with multiple answers.
Here's our template with sample CSV with fake data your can try uploading, or use as a starting point for your own data.
Handling multiple answers for a single question
You'll need Google Sheets or Excel 2016 or later, so you can use the TEXTJOIN formula, which lets you specify semicolon as the separator, and quickly take answers from multiple columns and get them into one column. Here's the Excel help and here's the Google Sheets help. Before you begin, search for any semicolons in your data and replace them all with something else like /.
In practical terms, let's say your spreadsheet has answers that span multiple columns and look like this:
You would then add this formula:
And now duplicate that on all your rows and voila, you have a new column with answers separated by semicolon: