confused about groups

I've created a spreadsheet that i want other people to be able to read/write. So, do I need to create a group and add the email addresses to that group. Then invite them to read/write the spreadsheet? Everyone needs to be able to see everything others have added. Is this correct?

I posted a link to my website, which brings up the spreadsheet, but it says it won't save the changes. I don't get it!