Drupal 7.x

Im new to drupal maybe anyone here can tell me straight up what they are for? And are they really necessary?

Thanks.

I have downloaded the drupal 7.x and when I am practicing I do not find the option permission in configuration what should i do to have this option in my administration pannel

I am new to Drupal and I want to use it to create a relatively easy website:
1) The visitor can sign up to join the website
2) The user can log in
3) There is going to be a/various database(s) with different types of data (i.e. pictures, text, metadata, etc.)
4) The user can upload/download pictures and data from the database
5) I want the database(s) to be able to encapsulate the data (pictures, text) so that they are not accessible by outside visitors in the form of http://blablabla.com/zoo.jpg

I'm looking for a possibility to schedule some short talks (about 10 minutes) for a group of people. I would like to know if such an specific module already exist, or whether the functionality could be made with several modules. I looked at some modules, like the calendar, event_manager, and bookings modules. As far as I could see they do not meet my requirements:

The use case is the following:
- Parents of a primary school pupil are invited twice a year to talk about their child in a short talk with the teacher
responsible for the pupil, the talks are often planned with a duration of 10 minutes
- The short talks are planned by the teacher, that is responsible for the before mentioned pupil
- So in a class with around 25 pupils, there are about 25 slots required of around 10 minutes
- These slots are of course spread over several days and weeks, so the teacher should be able to create the list
with available slots
- The available slots should be presented to the parents in a pick list. If a slot is chosen by a parent the slot is
e.g. marked reserved and can no longer be selected by other parents

I hope the use case is clear. I assume that this functionality will depend on organic groups in Drupal 6 and in Drupal it will depend on groups (I think). It would be nice if this functionality would be available in D7.

Give some example why would you add custom fields to a vocabulary.
Is it possible to add these fields as a fieldset in a content type.

D7 and a fluid width 100% theme -

Creating graphics/theme from scratch for a potentially busy news site, where blocks/regions/columns/rows are dynamic, place anything about anywhere / contents or ads;. Is it a good idea to use a parent theme/framework or just do your own 'div' thing. If using a framework what would be the best one. What about grid based design, are any of those available at 100% width; is there any performance issue on busy sites having grids. Looking at about 40-50 regions I guess.