Contexts are situations in which language is used.

Some examples:

Target language: Passive Voice

Example sentence:  "Three men have been arrested."

Useful context:  Newspaper articles

Language: Present Perfect for experiences

Example sentence:  "I have lived in several countries in Europe."

Useful context 1:  To talk about life experiences

Useful context 2:  A job interview

Langage: Present continuous for future arrangements

Example sentence:  "We're flying out next Monday morning."

Useful context 1:  Talking about holiday plans.

Useful context 2:  Arranging a business meeting.

Langage: Present continuous for an action in progress

Example sentence:  "She's playing tennis."

Useful context 1:  Explaining why someone is absent / not here.

Useful context 2:  Describing a scene in a picture or photo.

Do note that there are two different ways to think about context:

1) The immediate surroundings / the scene - who is talking to who, where are they, what are they doing now, what's happening in the background, etc.  I believe this is useful for motivation/engagement.

2) The language situation - what is the purpose, what is the topic, who is the audience, is it written or spoken, what has been said before in the same conversation/text.  I believe this is useful for highlighting differences between language that is typical of spoken or written English, formal or informal, technical or general, etc.