“Many grocers switched back to single-use plastic bags and prohibited customers from bringing their own reusable bags.” --- “One company marketing single-use menus online provides an estimate of how many throwaway menus might be needed.” What does it mean if an item is single-use?

means you can only use it once and it can not be reused.

Explanation:

to show how the cables work.

the present continuous is a verb tense which is mainly used to indicates that an action is in progress at the moment of speaking.  

it is formed using: person + verb to be (am/is/are) +verb + - ing form  

example: i am studying at this moment .

in addition, the present continuous is also used in order to express things that will or will not happen in the near future.

example: i am having dinner with some friends tonight.

the speaker sometimes   uses it   to express that an action is repeated and it causes irritation on the part of the speaker

example: my sister is constantly complaining about everything.