Why is my wordpress not able to add new themes or plug-ins? Im missing some features aswell but i dont know why

I have not downloaded Wordpress, im only using a link given to me by the person who was the designer. Im only logging in with wp-admin. I have watched tutorial videos on wordpress but still im not seeing the features that are meant to be there according to my research

the Wordpress ver is 5.4.2

please can someone help thanks