CSV stands for a
comma-separated values file. It just allows data to be saved in a tabular format, but it differs from an Excel or Google Spreadsheet file because the data is held in a text format, separated by commas, rather than in a tabular form with rows and columns. So, when you open it as a text file it looks like gobbledegook. When you open it with Excel or as a Google Spreadsheet or some other spreadsheet programme it will look just like a file saved in those formats and can be saved as one of those.
If you have a Google account (and I thought most people would) then you most likely have already been storing the passwords that you use online and wouldn't need to upload them via a csv. file.
I don't use any 'password manager' myself, however I have found it useful to look at the advice Google gives about the passwords that I am using. To do that simply click on the three vertical dots at the very right-hand end of the google search bar (after any extensions and link to your google account). On the new list that appears, rather than clicking on that "Password Manager - NEW", click instead on the old "More tools" that you'll find about 2/3's of the way down.
On the next new list that appears click on "Clear browsing data". A new list appears and you would need to click on the box "Clear Data" if you want to continue with that (and I suggest that you do that regularly) but you don't need to do that and can skip it by clicking on the "Cancel" box instead. That brings you to a new page called "Settings - Privacy and security".
That seems convoluted, but I don't know a quicker way to get there.
On the "Settings - privacy and security page" click the box marked "Chrome can help keep you safe from data breaches, bad extensions, and more - CHECK NOW"
This will make a number of security checks including on the websites, extensions and passwords you use. It will tell you any passwords that are not deemed secure enough, or where you have used the same passwords several times. You then have an opportunity to change them for more secure passwords.