Stocks, Options, and ETFs are taxed as capital gains and capital losses. Short term capital gains (where most traders would be classified) are taxed at current income tax rates. Capital losses can be used to offset capital gains only and you cannot carry back capital losses. You are limited to $3,000 deduction on capital losses. Any excess loss gets carried forward to the next tax year.
Not sure what a capital gain or capital loss is? Not sure your current income tax bracket? Refer to this post.