Well, this word can be a verb or a noun.
As a verb, it means 2 main things:
1 - to be about something - "This report is concerned with Climate Change", "This report is about Climate Change".
2 - to be anxious or worried - "I am concerned about my test scores this year", "I am worried about my test scores this year"
As a noun, it can mean the cause of the anxiety or worry: "My concern is that I will never be good at English". OR, something that is of interest or importance to somebody, "Internet speed is a concern to us all".
Hope this helps!