You are quite correct, Eunice, to suggest that concern and its related forms are used in a variety of different ways. Here are some of the most important.

concerned (adj) = worried

Note the different ways in which the adjectival form is used:

• Why do you keep ringing me? ~ Well, I'm concerned about you. Are you all right?
  
  
• I was very concerned that my daughter might not have proper clothing for the skiing trip.
  
  
• I was concerned for her safety as well. There have been a lot of avalanches recently.
  
  
• There was a concerned expression on his face. I knew something awful had happened.
  

it concerns me = it worries me

Note that when concern is employed as a verb in this way, it cannot be used in the first or second person and it is normally used with the preparatory subject it. Note also that concern is not normally used with progressive forms. We need to indicate the idea of progression in some other way. Compare the following:

• It concerns me that she'll be in London for a whole week on her own.
  
  Rather than:
• That she'll be in London for a whole week on her own concerns me).
  
  
• Doesn't it concern you? She's only nineteen.
  
  
• The pollution problem in that part of the river is beginning to concern all the local anglers.
  

concern (noun) = worry

When concern is used as a noun, it expresses worry about a situation:

• There is growing concern that the climbers may have lost their lives.
  
  
• He expressed deep concern about the way in which the elections had been held.

concern (verb) / concerning (prep) = aboutWhen you use concern or concerning in this way, you are indicating what a question or a topic is about. Concerning and relating to are the formal equivalents of the much more informal about.

Compare the following:

Why are you arguing? What's it all about? What does it concern?

• ~ It's about the long lunch breaks enjoyed by the senior executives.
  
  
• ~ It concerns the long lunch breaks enjoyed by the senior executives.
  
  
• For information concerning / relating to opening hours during the summer months, contact the club secretary.
  
  
• If you want to know about opening hours in the summer months, give Joan a ring.
  
  
• A number of questions had been tabled relating to / concerning the dangers of the new vaccine.
  
  
• We had a lot of questions about people's concerns about the new vaccine.
  

concerned as past participle = involved / affected

The participle modifies the noun or pronoun in these examples and can be used instead of a participle clause:

• There was a brawl outside the nightclub. Those concerned were held in custody overnight. / The youths (who were) involved were held in custody overnight.
  
  
• Many have lost their savings. The pensioners concerned will receive substantial compensation / The pensioners who are affected by this will receive compensation.

as far as I'm concerned = in my opinion

When you want to express an opinion, you can use this formula as an alternative to in my view or in my opinion:

• As far as I'm concerned / In my view / In my opinion, the English football supporters should not be held responsible for starting the fight.

as far as x is concerned = concerning x

You can use these expressions to introduce the topic that you wish to talk about or the issue you want to refer back to - i.e. it may have been raised once already and you, as the current speaker, want to return to that topic. As far as x is concerned is a bit less formal than concerning x:

• As far as foreign languages are concerned, I think they should be taught in primary schools.
  
  
• Concerning foreign languages, in my view it is appropriate to teach them at primary school level.