This article is a simple explanation of the use of the Site.Login() Apex method. The documentation in detail from Salesforce is here http://www.salesforce.com/us/developer/docs/apexcode/Content/apex_classes_sites.htm.

STEP 1:
Enable Communities by going to the below path, Your Name -> Setup ->  App Setup -> Customize -> Communities -> Settings




STEP 2:
Create a new Community as shown below



STEP 3:
Create a Apex Class as shown below


Note: Replace 'null' with the URL to be redirected to after login.

STEP 4:

Create a Visualforce page 'CustomLoginPage' as shown below



STEP 5:
Navigate to Manage Communities from the setup menu, and click the 'Force.com' link as below



STEP 6:

Make the following changes as shown below.

STEP 7:

Modify the Apex Class 'CommunitiesLoginController' as below



STEP 8:

Modify the Visualforce page 'CommunitiesLogin' as below



STEP 9:

Make sure you publish the community. Navigate to the URL and you should see the custom login page as below.

A wrapper class is simply put a class which wraps variables of different data types into one single type.

We use List(account), List(string), List(integer) etc. But, what do you do when you want to create a list of all these three data types into one single list? That is when a wrapper class comes into help. Below is a simple code snippet to help understand this concept.

VF Page: 

Apex Class: 

Analyzing the code:

 The Wrapper Class in our example is named 'sampleWrapperClass'. Every wrapper class has two parts. One part to declare the variables, and the other part to define the constructor for the class. In our example, we have only one constructor. However, you can have multiple constructors by altering the parameters based upon your needs. Note that we have created a list which holds Integer,String,Boolean,Account,Contact datatypes together into one single custom data type called 'sampleWrapperClass'. You can then process this List as any other normal list. In our Visualforce page we display the list using a pageBlockTable.

Practical Examples: 

I took down some notes while preparing for the DEV 501 objective exam (first level). Though it might not be that the questions are based out of this notes, i am sure that you will find these useful.

Comparison (triple =)

x === y, check reference. Check's whether the reference between the objects x and y is the same.

Collections in apex:

list - ordered, non unique
set - unordered, unique
map - unordered, key value pair

Check this link for a detailed description. - Click here

Variable types:

static - lifetime is throughout the entire execution context

final - value can be set only once (public static final Integer example = 1)

Query clauses:

ALL ROWS - returns all rows including those in the recycle bin and archived activities
(Ex: System.assertEquals(2, [SELECT COUNT() FROM Contact WHERE AccountId = a.Id ALL ROWS]);)

FOR UPDATE: locks the record for update from other means while the execution is happening.
(Ex:  Account [] accts = [SELECT Id FROM Account LIMIT 2 FOR UPDATE]; )

 Salesforce Query Language:

SOQL - returns a list of sObjects.
SOSL - returns a list of list of sObjects. This is because SOSL queries can query multiple objects.

DYNAMIC BINDING:
Treats the characters after ':' as executable Apex Code.

EXTERNAL ID: NOT unique by default

Webservice methods cannot be overloaded.

Case, switch statements not available in apex as of now. Use nested, IF- ELSE to accomplish this.

Three types of FOR loops:

1) for (integer i=0; i<100 i="" p="">
2) for (Integer i : List)

3) for (Account a: [Select Id from Account where Name != 'Edwin'])
    for (List accts : [SELECT id, name FROM account
                                                                               WHERE name LIKE 'Acme']) - Querymore mode


Apex Manual Sharing:
Row Cause: Can create custom row cause from the 'Apex Sharing Reasons' related list on the custom object. Ex: Schema.Object__Share.RowCause.Rowcausename__c

Access: Read, Edit, Full (this is only for owner and cannot be set for other users)

Field: IsDeleted = TRUE, indicates records in the recycle bin

Different database operations:
INSERT UPSERT UPDATE DELETE MERGE UNDELETE

database.dmloptions - Ex: truncation (text fields exceeding max limit- truncate or throw error)

database.setsavepoint()
datase.rollback(savepointname)

You can have a maximum of upto 5 savepoints.
No explicit COMMIT statement, commit happens implicitly at the end of the transaction.

Different types of trigger events:

before insert
before update
after insert
after update
before delete
after delete
after undelete

if you have 4 different triggers on say the 'before insert' event, there is no guarantee on the execution order of the triggers

Merge event - delete on losing record, update on winning record


Cascade DELETE - if a master record is deleted the trigger fires on the master record, however even though the detail records are deleted the trigger does not fire on the detail records.

String comparison in apex: uppercase A is different from lowercase a

Exception Handling:

try {throw} catch (){} finally{}

public class MyException extends Exception{}

//try, throw and catch
     try {
         Integer i;
         //Your code here
         if ( i < 5 ) throw new MyException();
    } catch ( MyException e ) {
         //Your MyException handling code here
    }
    finally { system.debug('executes no matter what');}

############### Apex Code Developer's Guide##########################
Custom Labels: Accessed using the notation System.Label.Label_Name

If You have Person Accounts enabled and you insert an Account using (name='xxx') a Business Account is created. If you insert a account using (Lastname ='yyy') a person account is created.

Relationship tip:
When being read as a value, if c.Account is null, then c.Account.Name evaluates to null,but does not yield a NullPointerException.
When being modified, if c.Account is null, modifying c.Account.Name does yield a NULL pointer exception.

A LIST can contain unto four levels of nested lists.

Use the Comparable interface to implement a custom sort for Lists.