Tax for short term stock gains

Stock is a capital asset and you will be liable to "Short term capital gain" since it was sold within a year.

You can give these details to your employer and they can deduct tax accordingly

Alternatively you can also pay self assessment tax u/s 140A on this by using challan No. 280

Online Payment ?

 https://onlineservices.tin.egov-nsdl.com/etaxnew/tdsnontds.jsp

No documents are required to be submitted while filing the return, the AO can ask these documents when he may require

Am further citing S. 48 for the computation purpose

" S. 48

The income chargeable under the head "Capital gains" shall be computed, by deducting from the full value of the consideration received or accruing as a result of the transfer of the capital asset the following amounts, namely :—

(i) expenditure incurred wholly and exclusively in connection with such transfer;

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