Since you have got your form 16 from your employer for the previous year, which i think, in your case is 2011-12.
As far as question regarding attachment goes, i think you must have already furnished all the attachments to your employer, who in turn would have taken it into consideration in providing you with the requisite deductions and thereafter deducted tax on the remaining taxable income. therefore there is no need to attach anything along with the income tax return. In addition it is also not allowed to provide any attachment along with your return whether you file it manually or online.
But in case you have forgot to provide any information before issuing form 16 to your employer regarding your savings like forgot to give the premium receipt of your life insurance or medical insurance, then you will have to take that deduction into consideration and recompute your tax accordingly.
Now coming to Income tax return. In this case you will need the Form 16 issued to you and the income tax return form applicable to you. Assuming that you have only salary and interest income, ITR 1 or Sahaj is applicable to you. You need to fill the details as mentioned in form 16 regarding your taxable salary, deductions and tax deducted and other information as asked in Sahaj form.
In case you have recomputed your income as told to you above when any saving details were not provided and benefit of which is available, then you should fill the Sahaj form on basis of new computation. In such case you can take help of any agent or professional if you are not aware of the process to compute tax and take deductions, which i assume you must be very much aware.
Now comes the filing part of return. you can file your income tax return in two ways:
1. In manual method you will have to take printout of the Sahaj form and fill all details manually and sign the same and go to your applicable ward to file the return by hand and take acknowledgement there and the. If you are not aware of your ward then you can check the same from income tax site by filling your PAN no. Link for same is given as reference.
2. In online method you have to follow the given procedure.
a) Got to incometaxindiaefiling.gov.in and download the Sahaj form by selecting the coorect assessment year i.e. 2012-13
b) Fill the form as per the details given in form 16. make sure all the information is provided.
c) Generate xml by clicking the button given in the form (sahaj) and save the same.
d) Now go to the site address given above and register your PAN if not done already.
e) Now after registering your PAN you can login to your account on the site and file your return.
Till last year, after filing your return online one had to take printout of ITR V which gets generated after filing of return and sign it and send it to CPC Banglore, which will be scrapped from this year onwards as proposed. The Income tax department is working on the same.
Now you can choose between the methods most appropriate to you.
With regard to tax refund, it is possible only in case tax deducted by employer is more than it should be. Generally the employer takes all the financial declaration from employees and then accordingly computes tax individually for each employee and later deduct tax only to the extent applicable to each employee. However there can be a difference in case any documents were not submitted in time as told above regarding any saving receipt not provided to employer.
Only in such cases you need to recompute income and fill the applicable ITR form and claim refund, but remember you do not need to attach any kind of proof along with the return. You should keep the receipts and new computation with you in case it is needed in future (which usually is not required).