Yes, depending on your plan there is the option to add up to 4 additional users to your account. Additional users can only be added and created by administrators. The account owner is always flagged as such.
There are two ways to add another user. You can add a new user if you click on Settings -> User & passwords.
The second way to add a new user is to click on your name on the top right. There, select "Your account". On the left of the next page, an option called "Users and passwords" is shown. Selecting this brings up the user management screen.
To add another user, simply click on "Add user" on the top right. In the popup, you have to fill in the user credentials and assign him access rights. Both credentials and rights can later be edited by selecting "Actions" next to the user FTP password column.
Please note: If your current plan does not permit additional users, an error message indicating this will be displayed.