If you e-filed your tax return you do not send your W-2 to the IRS. If they want a copy of your W-2 they will send a letter asking for it, but that is very rare.
If you filed by mail and forgot to attach your W-2, do not send it now. Wait and see if the IRS asks for it. If they want a copy of your W-2 they will send a letter asking for it. Follow the instructions in the letter for how to send the W-2.
Or do you mean that you filed your tax return but did not include the income from your W-2? If that's what happened, you have to wait until the IRS has processed your tax return and you have received the refund. Then you will have to file an amended return, Form 1040-X, to add the income that you omitted.