Selling stocks will affect your income taxes. If you are going through a broker or financial advisor, he should be able to briefly explain the tax information for you, but it is still your responsibility to have the correct paperwork on hand. If you are using an online brokerage site, then you need to make sure that you keep all receipts for the purchase and the sales of the stocks.
When you sell your stocks, you are taxed on the profit of the stocks. If you sell at a lost, you can claim a loss on your taxes. For this reason you need to keep a receipt of the purchase of the stocks. If your stocks have split, you take your purchase price, and divide it by the number of shares you have now to determine the value to be assigned to each individual stock. When you sell you subtract the purchase price from the sell price. The result is the number you report on your taxes.
If the number is positive, then you are reporting a capital gain. If you bought the stocks and then sold them within a year of the purchase date, then the amount is added to your regular income, and is taxed at the same rate as your income. However if it has been more than a year the amount is taxed at the capital gains rate, which is lower than most income tax rates. If you can hold onto the stocks for a year, you can save a lot in taxes. It is possible to claim both long term and short-term gains in the same tax year.
If the number is negative, then you are reporting a capital loss. You can claim a capital loss on your taxes as well. This is process has very specific guidelines that must be followed. You should talk to an accountant about how to claim this as well. You will still need the original receipt for the price that you purchased, and then the receipt of the sale to show how much you lost. You should do this even if you purchase them through stock options at your job.
If you are trying to lower the amount of taxes that you pay on your investment, it is best to wait a year before selling the stocks. This will lower your tax liability while allowing you to profit from your stocks. It is always important to keep records of your purchases of stocks so that you can correctly claim then on your taxes.