If you say someone is concerned, it means that person is worried:
I'm concerned about my son - he's not getting good grades in school.
I live in a big city, and my mother is concerned for my safety.
We're concerned that we won't be able to finish the project in time.
You can also say "it concerns me" to talk about something that worries you:
I've had a stomachache for the past three days. It's starting to concern me.
It concerns me that the teachers don't seem interested in helping the students.
The noun concern means "a worry":
Sheila is going to marry an ex-convict. Her father has deep concerns about the relationship.
There is growing concern that the country's economy may enter into a recession.
I have a few concerns about this contract - it doesn't seem like a good deal.
The word concerning means something completely different - it means "relating to" or "about."
Please visit your local bank for more information concerning your account. "Concerning" is a bit formal - in everyday English we typically use "about":
Formal: There were a number of questions concerning the new program.
Informal: There were a number of questions about the new program.
When concerned is used as a past participle (after the subject), it means "involved" or "affected":
There was a big fight at the bar. The police talked with everyone concerned. (Everyone involved in the incident)
After a defect was discovered in the manufacturing process, the products concerned were recalled. (The products affected by the defective process)