The possibility of granting rights to other users is available only for logged in users. You will find the list in the menu on the right side if you click on your name and there click on "grant to users".
In this page you can grant rights to other users. You can only grant rights for persons which were created by you. First choose the user to whom you want to grant a right. Second choose the dimension of granting: The person which was last selected or all own persons. After that choose the type of grant: read only or read and write. Finally click on the button "grant" to grant this right.