When you created a space, you received a letter in your mail that contains two formats of links to your space.
One of them is the Space link. It looks like this:
There are no additional characters after the name of the space.
This is the link you should send to your members, and they will be able to enter the space.
The second Space admin link looks like this:
With a question mark and password. If you give someone such a link, that member will have administrator rights.