Hi Bhanu,

Please find the below explanation ....................

Page Layouts :

Page layouts control the layout and organization of buttons, fields, s-controls, Visualforce, custom links, and related lists on object record pages. They also help determine which fields are visible, read only, and required. Use page layouts to customize the content of record pages for your users.
Control which fields, related lists, and custom links users see, on detail and edit pages only.
Control which standard and custom buttons display on detail pages and related lists.
Determine whether fields are visible, read only, or required, on detail and edit pages only.
Determine the fields that users can import data into.
Available in: both Salesforce Classic and Lightning Experience . Page layouts are available in: All Editions

Creation and deletion of page layouts is available in: Enterprise, Performance, Unlimited, and Developer Editions

User Permissions NeededTo create, edit, and delete page layouts:“Customize Application”

Page layouts can include s-controls and Visualforce pages that are rendered within a field section when the page displays. You can control the size of the s-controls and Visualforce pages, and determine whether or not a label and scroll bars display.

Salesforce has two drag-and-drop tools for editing page layouts: the original page layout editor and an enhanced page layout editor. The enhanced page layout editor is enabled by default, and provides all the functionality of the original editor, as well as additional functionality and an easier-to-use WYSIWYG interface.

In Professional, Enterprise, Performance, Unlimited, and Developer Editions, you can set the mini page layouts and related objects that appear in the Console tab.

See Also the above links for more information :

https://help.salesforce.com/HTViewHelpDoc?id=customize_layoutoverview.htm&language=en_US
https://help.salesforce.com/HTViewHelpDoc?id=accessing_layout_standard.htm&language=en_US
https://help.salesforce.com/HTViewHelpDoc?id=accessing_layout_custom.htm&language=en_US

Validation Rules : 

Validation rules verify that the data a user enters in a record meets the standards you specify before the user can save the record. A validation rule can contain a formula or expression that evaluates the data in one or more fields and returns a value of “True” or “False”. Validation rules also include an error message to display to the user when the rule returns a value of “True” due to an invalid value.

After you have defined validation rules:

The user chooses to create a new record or edit an existing record.
The user clicks Save.
All validation rules are verified.
If all data is valid, the record is saved.
If any data is invalid, the associated error message displays without saving the record.
The user makes the necessary changes and clicks Save again.

You can specify the error message to display when a record fails validation and where to display it. For example, your error message can be “The close date must occur after today's date.” You can choose to display it near a field or at the top of the page. Like all other error messages, validation rule errors display in red text and are preceded by the word “Error”.

See Also the above links for more information :

https://help.salesforce.com/HTViewHelpDoc?id=fields_defining_field_validation_rules.htm&language=en_US
https://help.salesforce.com/HTViewHelpDoc?id=fields_validation_rules_fields.htm&language=en_US
https://help.salesforce.com/HTViewHelpDoc?id=fields_useful_field_validation_formulas.htm&language=en_US


Data Loader :

The Data Loader is an easy to use graphical tool that helps you to get your data into Salesforce objects. The Data Loader can also be used to extract data from database objects into any of the destinations mentioned above. You can even use the Data Loader to perform bulk deletions by exporting the ID fields for the data you wish to delete and using that source to specify deletions through the Data Loader.

The Data Loader requires the use of the Force.com API. If your Salesforce edition allows the use of the API (Enterprise, Unlimited and Developer Editions), you can download the Data Loader from the Setup menu, under Administer heading -Data Management.

Features of data loader :

a)An easy-to-use wizard interface for interactive use
b)An alternate command-line interface for automated batch operations (Windows only)
c)Support for large files with up to 5 million records
d)Drag-and-drop field mapping
e)Support for all objects, including custom objects
f)Can be used to process data in both Salesforce and Database.com
g)Detailed success and error log files in CSV format
h)A built-in CSV file viewer
i)Support for Windows XP, Windows 7, and Mac OS X

To get started, see the following links:

https://help.salesforce.com/apex/HTViewHelpDoc?id=when_to_use_the_data_loader.htm&language=en_US
https://help.salesforce.com/apex/HTViewHelpDoc?id=installing_the_data_loader.htm&language=en_US
https://developer.salesforce.com/page/Data_Loader_Video

Please let me know if this helps you.............................


Thanks & Regards
Nagendra.P
9848950830