I have the task of creation of the exhibition themes diving spearfishing, etc.

and so the essence of the problem - the creation of a directory of participants

Registered users (the company) has its own card - a page on which the following information:
photo shoot
description
contact information
website
Additional information (stand)
news (news list title, kartnka, entry)

Do not need a filter authors (companies) in alphabetical order ie when you click on the letter A list of participants falls beginning with A (English or Russian as easier)
next on the list now shows the text - stand number (active link)

when you press the number of the stand there is a transition to the link (as planning or implemented through the card or third-party solutions)
By clicking on the name of the company to get a card showing the contacts and the bottom of this company news
www.demashow.com/dema2015/public/Exhibitors.aspx?ID=9078&sortMenu=104002#


admin logs the user, then the user edits the other fields on their own and independently
creates news that are published on the page the user Something like twitter (text, photos, video)
and through the module published somewhere on the website (latest news), when you click on the author, the visitor gets to the user's page.

thought the use of K2, but do not quite understand how to do it.

Well, as for any exhibition, all users are divided into four main areas (thought to use it through tags)
example:

cars
Motorcycles
led
- Click on the car, drop us a list of all who are engaged in or related to cars:
A tire 100
F-12 parts

well, etc.
click on the name to get a card
click on the number - get on the floorplan where noted this company

some companies may be in several sections, ie, prescribes both tag

need help with the implementation of the idea.

This seems like a custom project where a dev or an agency should be contracted.
We can offer some info on specific but we cannot provide a complete project analysis.

Possible.
This is one of the tasks
if you can solve this problem I would like to know the cost.
If not difficult

With the search is difficult because they do not know option for solving the problem.
everything comes down to the list of authors who will lead the publication of news

It would be unprofessional of me to accept jobs from the forum.
However I am happy to provide you a list with companies and talented individuals that are working with K2.

Here's a list of Joomla / K2 expert companies we recommend (in no particular order):
ideasencoded.gr (GR)
internet-inspired.com (UK)
joomla-agentur.de (DE)
manoscrafted.com (USA)
pbwebdev.com (AU)
thinksync.com.au (AU)
www.3bweb.com (UK)
www.aboutnet.gr (GR)
www.acs-digital.com (USA)
www.dreamcube.gr (GR)
www.exis.com.gr (GR)
www.intros.gr (GR)
www.itoctopus.com (USA)
www.jiliko.net (FR)
www.keegot.com (GR)
www.piezoworks.be (BE)
www.raramuridesign.com (ZA)
www.zott.ag (BR)
y-designs.com (USA)