To share a file click on this symbol < to the right of the file name
in the name or email box enter the email address of who you wish to share the file with
you can then decide if you wish the person(s) to be able to read only or be able to edit
if you wish them to be able to edit the file click on the tick box
To share a folder click on this symbol < to the right of the folder name
in the name or email box enter the email address of who you wish to share the folder with
you can then decide if you wish the person(s) to be able read only, to be able to create, be able to edit, be able to delete
then click on the three dots next to can edit and tick or untick the relevant box(es)