Hey Vijay ,
 RecordType is a object in salesforce . 
We can categories records in one object by creating recordtype in that object .
Once you will create a record type in one object it will create a record in RecordType object with SobjectType of that Object .
e,g If you have created a record type in Account so in RecordType object it will create a record with Sobject type as Account 
and Developer name as recordtype api name as record type name .You can query and check in work bench for this reason we can create same record type in different object .
While creating record type we have to assign a page layout to that . Also we can restrict picklist values with help of record type means if in a picklist you have 10 values 
if you want to dispaly 5 valu ein one record type and other five in next record type that also you can do .
In standrad object if already any pick list is there so salesforce have already created some process for that ,If you want to assign different value for record type then you 
need to modify that process .
If you have 5 record type in your object but you want to dispay only 3 to on eprofile that you can do in profile level .

let me know any doubt you have regarding record type .