Q:

What is res.partner?

I am new to openerp I came across res.partner but I couldn't understand what it does and what all functionalities it provides,so if anyone could explain it to me I would be grateful.

A:

To clarify.
res.partner is an ORM Model.  An ORM model describes a class of objects in the database and provides a series of ORM methods to allow you to manage them in code (create, write, unlink etc).
To get the database table, unless there is a specific _table override, just convert the periods to underscores so the table in the database is res_partner.  As with any "res." model, you get res.partner as part of the core of OpenERP rather than any additional model such as accounting or sales.
But to answer a wider question, what is res.partner for in OpenERP?  Assuming OpenERP 7,  res.partner contains information about any entities you have a relationship with.
This includes:

Customers - you have a res.partner entry for each customer plus a res.partner entry for each contact person or address (invoice to, deliver to) you set up for that customer.
Suppliers - same as customers.  In fact, the only difference between the two is a boolean field on res.partner to say if they are a customer or supplier.
Users - each user allowed to log in to your OpenERP instance has a related res.partner to store address details.
Companies - each company you set up in OpenERP assuming you are using multi-company has a related res.parter to store address details.

A:

res.partner is the technical name for the Model representing Partners:
Partners represent People and Organizations.
The most straightforward example are Customers and Suppliers. 
Other examples of Partners are:

Contact persons within an organization
Customer or Supplier Adresses
Employees personal contact data
Users contact data

So it's a base concept used pretty much everywhere in the application.

