There is 2 ways of inviting people to joint your team. You can invite them directly by email or you can send a general invitation link directly to them.
If you want to invite people by email you can go to the teams page, after that you can click on "Invite members by email".
You should add everyone you want to invite. And click on "Invite members".
After you type your team members and click on "Invite Members", they will show on your team as "Pending" members.
Another way of inviting people is by generating a general invite link and sending that on your team chat for example. To create a link you can click on "Generate invite link".
After that you can copy by clicking on "Copy invite link" and pasting it on your team chat or sending it by email.
After this people will need to open the link they received by email or sent by you, register an account on funretro and join the team. You will be able to see everyone that joined on your teams page.